fs-util: rename path_is_safe() → path_is_normalized()

Already, path_is_safe() refused paths container the "." dir. Doing that
isn't strictly necessary to be "safe" by most definitions of the word.
But it is necessary in order to consider a path "normalized". Hence,
"path_is_safe()" is slightly misleading a name, but
"path_is_normalize()" is more descriptive, hence let's rename things
accordingly.

No functional changes.

src/basic/cgroup-util.c

@@ -1278,7 +1278,7 @@ int cg_split_spec(const char *spec, char **controller, char **path) {
         assert(spec);
 
         if (*spec == '/') {
-                if (!path_is_safe(spec))
+                if (!path_is_normalized(spec))
                         return -EINVAL;
 
                 if (path) {
@@ -1331,7 +1331,7 @@ int cg_split_spec(const char *spec, char **controller, char **path) {
                         return -ENOMEM;
                 }
 
-                if (!path_is_safe(u) ||
+                if (!path_is_normalized(u) ||
                     !path_is_absolute(u)) {
                         free(t);
                         free(u);