tree-wide: make FOREACH_DIRENT_ALL define the iterator variable

The variable is not useful outside of the loop (it'll always be null
after the loop is finished), so we can declare it inline in the loop.
This saves one variable declaration and reduces the chances that somebody
tries to use the variable outside of the loop.

For consistency, 'de' is used everywhere for the var name.

src/basic/fs-util.c

@@ -533,7 +533,6 @@ int mkfifoat_atomic(int dirfd, const char *path, mode_t mode) {
 int get_files_in_directory(const char *path, char ***list) {
         _cleanup_strv_free_ char **l = NULL;
         _cleanup_closedir_ DIR *d = NULL;
-        struct dirent *de;
         size_t n = 0;
 
         assert(path);