commit: remove find_header_mem()

cfc5cf428b (receive-pack.c: consolidate find header logic, 2022-01-06)
introduced find_header_mem() and turned find_commit_header() into a thin
wrapper.  Since then, the latter has become the last remaining caller of
the former.  Remove it to restore find_commit_header() to the state
before cfc5cf428b, get rid of a strlen(3) call and resolve a NEEDSWORK
note in the process.

Signed-off-by: René Scharfe <l.s.r@web.de>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit.c

@@ -1737,20 +1737,12 @@ struct commit_list **commit_list_append(struct commit *commit,
 	return &new_commit->next;
 }
 
-const char *find_header_mem(const char *msg, size_t len,
-			const char *key, size_t *out_len)
+const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
 {
 	int key_len = strlen(key);
 	const char *line = msg;
 
-	/*
-	 * NEEDSWORK: It's possible for strchrnul() to scan beyond the range
-	 * given by len. However, current callers are safe because they compute
-	 * len by scanning a NUL-terminated block of memory starting at msg.
-	 * Nonetheless, it would be better to ensure the function does not look
-	 * at msg beyond the len provided by the caller.
-	 */
-	while (line && line < msg + len) {
+	while (line) {
 		const char *eol = strchrnul(line, '\n');
 
 		if (line == eol)
@@ -1767,10 +1759,6 @@ const char *find_header_mem(const char *msg, size_t len,
 	return NULL;
 }
 
-const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
-{
-	return find_header_mem(msg, strlen(msg), key, out_len);
-}
 /*
  * Inspect the given string and determine the true "end" of the log message, in
  * order to find where to put a new Signed-off-by trailer.  Ignored are