builtin: remove USE_THE_REPOSITORY_VARIABLE from builtin.h

Instead of including USE_THE_REPOSITORY_VARIABLE by default on every
builtin, remove it from builtin.h and add it to all the builtins that
include builtin.h (by definition, that means all builtins/*.c).

Also, remove the include statement for repository.h since it gets
brought in through builtin.h.

The next step will be to migrate each builtin
from having to use the_repository.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/diff-files.c

@@ -3,13 +3,13 @@
  *
  * Copyright (C) Linus Torvalds, 2005
  */
+#define USE_THE_REPOSITORY_VARIABLE
 #include "builtin.h"
 #include "config.h"
 #include "diff.h"
 #include "diff-merges.h"
 #include "commit.h"
 #include "preload-index.h"
-#include "repository.h"
 #include "revision.h"
 
 static const char diff_files_usage[] =