branch -m/-M: remove undocumented RENAMED-REF

The commit message for c976d41 (git-branch: add options and tests for
branch renaming, 2006-11-28) mentions RENAME_REF but otherwise this is not
documented anywhere, and it does not appear in any of the tests.

Worse yet, the name of the actual file is "RENAMED-REF".

This was supposed to hold the commit object name at the tip of the branch
the most recent "branch -m/-M" renamed, but that is not necessary in order
to be able to recover from a mistake. Even when "branch -M A B" overwrites
an existing branch B, what is kept in RENAMED-REF is the commit at the tip
of the original branch A, not the commit B from the now-lost branch.

Just remove this unused "feature".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -786,7 +786,6 @@ int delete_ref(const char *refname, unsigned char *sha1)
 
 int rename_ref(const char *oldref, const char *newref)
 {
-	static const char renamed_ref[] = "RENAMED-REF";
 	unsigned char sha1[20], orig_sha1[20];
 	int flag = 0, logmoved = 0;
 	struct ref_lock *lock;
@@ -809,13 +808,6 @@ int rename_ref(const char *oldref, const char *newref)
 	if (snprintf(msg, sizeof(msg), "renamed %s to %s", oldref, newref) > sizeof(msg))
 		return error("Refnames to long");
 
-	lock = lock_ref_sha1_basic(renamed_ref, NULL, NULL);
-	if (!lock)
-		return error("unable to lock %s", renamed_ref);
-	lock->force_write = 1;
-	if (write_ref_sha1(lock, orig_sha1, msg))
-		return error("unable to save current sha1 in %s", renamed_ref);
-
 	if (log && rename(git_path("logs/%s", oldref), git_path("tmp-renamed-log")))
 		return error("unable to move logfile logs/%s to tmp-renamed-log: %s",
 			oldref, strerror(errno));