Make fopen_temporary and fopen_temporary_label unlocked

This is partially a refactoring, but also makes many more places use
unlocked operations implicitly, i.e. all users of fopen_temporary().
AFAICT, the uses are always for short-lived files which are not shared
externally, and are just used within the same context. Locking is not
necessary.

src/basic/env-file.c

@@ -1,7 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
-#include <stdio_ext.h>
-
 #include "alloc-util.h"
 #include "env-file.h"
 #include "env-util.h"
@@ -545,7 +543,6 @@ int write_env_file(const char *fname, char **l) {
         if (r < 0)
                 return r;
 
-        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod_umask(fileno(f), 0644);
 
         STRV_FOREACH(i, l)