cache.h: remove this no-longer-used header

Since this header showed up in some places besides just #include
statements, update/clean-up/remove those other places as well.

Note that compat/fsmonitor/fsm-path-utils-darwin.c previously got
away with violating the rule that all files must start with an include
of git-compat-util.h (or a short-list of alternate headers that happen
to include it first).  This change exposed the violation and caused it
to stop building correctly; fix it by having it include
git-compat-util.h first, as per policy.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -6,7 +6,7 @@
  */
 
 #define USE_THE_INDEX_VARIABLE
-#include "cache.h"
+#include "builtin.h"
 #include "advice.h"
 #include "config.h"
 #include "lockfile.h"
@@ -15,7 +15,6 @@
 #include "dir.h"
 #include "editor.h"
 #include "environment.h"
-#include "builtin.h"
 #include "diff.h"
 #include "diffcore.h"
 #include "commit.h"