treewide: remove unnecessary cache.h includes

We had several header files include cache.h unnecessarily.  Remove
those.  These have all been verified via both ensuring that
    gcc -E $HEADER | grep '"cache.h"'
found no hits and that
    cat >temp.c <<EOF &&
    #include "git-compat-util.h"
    #include "$HEADER"
    int main() {}
    EOF
    gcc -c temp.c
successfully compiles without warnings.

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

checkout.h

@@ -1,7 +1,7 @@
 #ifndef CHECKOUT_H
 #define CHECKOUT_H
 
-#include "cache.h"
+#include "hash.h"
 
 /*
  * Check if the branch name uniquely matches a branch name on a remote

entry.h

@@ -1,9 +1,11 @@
 #ifndef ENTRY_H
 #define ENTRY_H
 
-#include "cache.h"
 #include "convert.h"
 
+struct cache_entry;
+struct index_state;
+
 struct checkout {
 	struct index_state *istate;
 	const char *base_dir;

khash.h

@@ -26,7 +26,6 @@
 #ifndef __AC_KHASH_H
 #define __AC_KHASH_H
 
-#include "cache.h"
 #include "hashmap.h"
 
 #define AC_VERSION_KHASH_H "0.2.8"

oidmap.h

@@ -1,7 +1,6 @@
 #ifndef OIDMAP_H
 #define OIDMAP_H
 
-#include "cache.h"
 #include "hashmap.h"
 
 /*

pretty.h

@@ -1,11 +1,11 @@
 #ifndef PRETTY_H
 #define PRETTY_H
 
-#include "cache.h"
 #include "date.h"
 #include "string-list.h"
 
 struct commit;
+struct repository;
 struct strbuf;
 struct process_trailer_options;
 

reflog-walk.h

@@ -1,8 +1,6 @@
 #ifndef REFLOG_WALK_H
 #define REFLOG_WALK_H
 
-#include "cache.h"
-
 struct commit;
 struct reflog_walk_info;
 struct date_mode;

refs/refs-internal.h

@@ -1,7 +1,6 @@
 #ifndef REFS_REFS_INTERNAL_H
 #define REFS_REFS_INTERNAL_H
 
-#include "cache.h"
 #include "refs.h"
 #include "iterator.h"
 

remote.h

@@ -1,7 +1,6 @@
 #ifndef REMOTE_H
 #define REMOTE_H
 
-#include "cache.h"
 #include "parse-options.h"
 #include "hashmap.h"
 #include "refspec.h"

sequencer.h

@@ -1,11 +1,11 @@
 #ifndef SEQUENCER_H
 #define SEQUENCER_H
 
-#include "cache.h"
 #include "strbuf.h"
 #include "wt-status.h"
 
 struct commit;
+struct index_state;
 struct repository;
 
 const char *git_path_commit_editmsg(void);

xdiff-interface.h

@@ -1,7 +1,7 @@
 #ifndef XDIFF_INTERFACE_H
 #define XDIFF_INTERFACE_H
 
-#include "cache.h"
+#include "hash.h"
 #include "xdiff/xdiff.h"
 
 /*