wrapper.c: remove unused git_mkstemp() function

The last caller of git_mkstemp() was removed in commit 6fec0a89
("verify_signed_buffer: use tempfile object", 16-06-2016). Since
the introduction of the 'tempfile' APIs, along with git_mkstemp_mode,
it is unlikely that new callers will materialize. Remove the dead
code.
Signed-off-by: NRamsay Jones <ramsay@ramsayjones.plus.com>
Reviewed-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

cache.h

@@ -1045,9 +1045,6 @@ static inline int is_empty_tree_oid(const struct object_id *oid)
 	return !hashcmp(oid->hash, EMPTY_TREE_SHA1_BIN);
 }
 
-
-int git_mkstemp(char *path, size_t n, const char *template);
-
 /* set default permissions by passing mode arguments to open(2) */
 int git_mkstemps_mode(char *pattern, int suffix_len, int mode);
 int git_mkstemp_mode(char *pattern, int mode);

wrapper.c

@@ -440,23 +440,6 @@ int xmkstemp(char *template)
 	return fd;
 }
 
-/* git_mkstemp() - create tmp file honoring TMPDIR variable */
-int git_mkstemp(char *path, size_t len, const char *template)
-{
-	const char *tmp;
-	size_t n;
-
-	tmp = getenv("TMPDIR");
-	if (!tmp)
-		tmp = "/tmp";
-	n = snprintf(path, len, "%s/%s", tmp, template);
-	if (len <= n) {
-		errno = ENAMETOOLONG;
-		return -1;
-	}
-	return mkstemp(path);
-}
-
 /* Adapted from libiberty's mkstemp.c. */
 
 #undef TMP_MAX