wrapper: reduce scope of remove_or_warn()

remove_or_warn() is only used by entry.c and apply.c, but it is
currently declared and defined in wrapper.{h,c}, so it has a scope much
greater than it needs. This needlessly large scope also causes wrapper.c
to need to include object.h, when this file is largely unconcerned with
Git objects.

Move remove_or_warn() to entry.{h,c}. The file apply.c still has access
to it, since it already includes entry.h for another reason.

Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wrapper.h

@@ -106,11 +106,6 @@ int unlink_or_msg(const char *file, struct strbuf *err);
  * not exist.
  */
 int rmdir_or_warn(const char *path);
-/*
- * Calls the correct function out of {unlink,rmdir}_or_warn based on
- * the supplied file mode.
- */
-int remove_or_warn(unsigned int mode, const char *path);
 
 /*
  * Call access(2), but warn for any error except "missing file"