treewide: remove cache.h inclusion due to git-zlib changes

This actually only affects http-backend.c, but the git-zlib changes
are going to be instrumental in pulling out an object-file.h which
will help with several more files.

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-backend.c

@@ -1,4 +1,4 @@
-#include "cache.h"
+#include "git-compat-util.h"
 #include "alloc.h"
 #include "config.h"
 #include "environment.h"