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/grep.c

@@ -3,7 +3,7 @@
  *
  * Copyright (c) 2006 Junio C Hamano
  */
-#include "cache.h"
+#include "builtin.h"
 #include "alloc.h"
 #include "gettext.h"
 #include "hex.h"
@@ -14,7 +14,6 @@
 #include "commit.h"
 #include "tag.h"
 #include "tree-walk.h"
-#include "builtin.h"
 #include "parse-options.h"
 #include "string-list.h"
 #include "run-command.h"