cocci: remove 'unused.cocci'

When 'unused.cocci' was added in 4f40f6cb73 (cocci: add and apply a
rule to find "unused" strbufs, 2022-07-05) it found three unused
strbufs, and when it was generalized in the next commit it managed to
find an unused string_list as well.  That's four unused variables in
over 17 years, so apparently we rarely make this mistake.

Unfortunately, applying 'unused.cocci' is quite expensive, e.g. it
increases the from-scratch runtime of 'make coccicheck' by over 5:30
minutes or over 160%:

  $ make -s cocciclean
  $ time make -s coccicheck
      * new spatch flags

  real    8m56.201s
  user    0m0.420s
  sys     0m0.406s
  $ rm contrib/coccinelle/unused.cocci contrib/coccinelle/tests/unused.*
  $ make -s cocciclean
  $ time make -s coccicheck
      * new spatch flags

  real    3m23.893s
  user    0m0.228s
  sys     0m0.247s

That's a lot of runtime spent for not much in return, and arguably an
unused struct instance sneaking in is not that big of a deal to
justify the significantly increased runtime.

Remove 'unused.cocci', because we are not getting our CPU cycles'
worth.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/coccinelle/tests/unused.c

@@ -1,82 +0,0 @@
-void test_strbuf(void)
-{
-	struct strbuf sb1 = STRBUF_INIT;
-	struct strbuf sb2 = STRBUF_INIT;
-	struct strbuf sb3 = STRBUF_INIT;
-	struct strbuf sb4 = STRBUF_INIT;
-	struct strbuf sb5;
-	struct strbuf sb6 = { 0 };
-	struct strbuf sb7 = STRBUF_INIT;
-	struct strbuf sb8 = STRBUF_INIT;
-	struct strbuf *sp1;
-	struct strbuf *sp2;
-	struct strbuf *sp3;
-	struct strbuf *sp4 = xmalloc(sizeof(struct strbuf));
-	struct strbuf *sp5 = xmalloc(sizeof(struct strbuf));
-	struct strbuf *sp6 = xmalloc(sizeof(struct strbuf));
-	struct strbuf *sp7;
-
-	strbuf_init(&sb5, 0);
-	strbuf_init(sp1, 0);
-	strbuf_init(sp2, 0);
-	strbuf_init(sp3, 0);
-	strbuf_init(sp4, 0);
-	strbuf_init(sp5, 0);
-	strbuf_init(sp6, 0);
-	strbuf_init(sp7, 0);
-	sp7 = xmalloc(sizeof(struct strbuf));
-
-	use_before(&sb3);
-	use_as_str("%s", sb7.buf);
-	use_as_str("%s", sp1->buf);
-	use_as_str("%s", sp6->buf);
-	pass_pp(&sp3);
-
-	strbuf_release(&sb1);
-	strbuf_reset(&sb2);
-	strbuf_release(&sb3);
-	strbuf_release(&sb4);
-	strbuf_release(&sb5);
-	strbuf_release(&sb6);
-	strbuf_release(&sb7);
-	strbuf_release(sp1);
-	strbuf_release(sp2);
-	strbuf_release(sp3);
-	strbuf_release(sp4);
-	strbuf_release(sp5);
-	strbuf_release(sp6);
-	strbuf_release(sp7);
-
-	use_after(&sb4);
-
-	if (when_strict())
-		return;
-	strbuf_release(&sb8);
-}
-
-void test_other(void)
-{
-	struct string_list l = STRING_LIST_INIT_DUP;
-	struct strbuf sb = STRBUF_INIT;
-
-	string_list_clear(&l, 0);
-	string_list_clear(&sb, 0);
-}
-
-void test_worktrees(void)
-{
-	struct worktree **w1 = get_worktrees();
-	struct worktree **w2 = get_worktrees();
-	struct worktree **w3;
-	struct worktree **w4;
-
-	w3 = get_worktrees();
-	w4 = get_worktrees();
-
-	use_it(w4);
-
-	free_worktrees(w1);
-	free_worktrees(w2);
-	free_worktrees(w3);
-	free_worktrees(w4);
-}

contrib/coccinelle/tests/unused.res

@@ -1,45 +0,0 @@
-void test_strbuf(void)
-{
-	struct strbuf sb3 = STRBUF_INIT;
-	struct strbuf sb4 = STRBUF_INIT;
-	struct strbuf sb7 = STRBUF_INIT;
-	struct strbuf *sp1;
-	struct strbuf *sp3;
-	struct strbuf *sp6 = xmalloc(sizeof(struct strbuf));
-	strbuf_init(sp1, 0);
-	strbuf_init(sp3, 0);
-	strbuf_init(sp6, 0);
-
-	use_before(&sb3);
-	use_as_str("%s", sb7.buf);
-	use_as_str("%s", sp1->buf);
-	use_as_str("%s", sp6->buf);
-	pass_pp(&sp3);
-
-	strbuf_release(&sb3);
-	strbuf_release(&sb4);
-	strbuf_release(&sb7);
-	strbuf_release(sp1);
-	strbuf_release(sp3);
-	strbuf_release(sp6);
-
-	use_after(&sb4);
-
-	if (when_strict())
-		return;
-}
-
-void test_other(void)
-{
-}
-
-void test_worktrees(void)
-{
-	struct worktree **w4;
-
-	w4 = get_worktrees();
-
-	use_it(w4);
-
-	free_worktrees(w4);
-}

contrib/coccinelle/unused.cocci

@@ -1,43 +0,0 @@
-// This rule finds sequences of "unused" declerations and uses of a
-// variable, where "unused" is defined to include only calling the
-// equivalent of alloc, init & free functions on the variable.
-@@
-type T;
-identifier I;
-// STRBUF_INIT, but also e.g. STRING_LIST_INIT_DUP (so no anchoring)
-constant INIT_MACRO =~ "_INIT";
-identifier MALLOC1 =~ "^x?[mc]alloc$";
-identifier INIT_ASSIGN1 =~ "^get_worktrees$";
-identifier INIT_CALL1 =~ "^[a-z_]*_init$";
-identifier REL1 =~ "^[a-z_]*_(release|reset|clear|free)$";
-identifier REL2 =~ "^(release|clear|free)_[a-z_]*$";
-@@
-
-(
-- T I;
-|
-- T I = { 0 };
-|
-- T I = INIT_MACRO;
-|
-- T I = MALLOC1(...);
-|
-- T I = INIT_ASSIGN1(...);
-)
-
-<... when != \( I \| &I \)
-(
-- \( INIT_CALL1 \)( \( I \| &I \), ...);
-|
-- I = \( INIT_ASSIGN1 \)(...);
-|
-- I = MALLOC1(...);
-)
-...>
-
-(
-- \( REL1 \| REL2 \)( \( I \| &I \), ...);
-|
-- \( REL1 \| REL2 \)( \( &I \| I \) );
-)
-  ... when != \( I \| &I \)