Rename strv_split_extract() to strv_split_full()

Now that _full() is gone, we can rename _extract() to have the usual suffix
we use for the more featureful version.

src/basic/env-util.c

@@ -687,7 +687,7 @@ char **replace_env_argv(char **argv, char **env) {
                         if (e) {
                                 int r;
 
-                                r = strv_split_extract(&m, e, WHITESPACE, EXTRACT_RELAX|EXTRACT_UNQUOTE);
+                                r = strv_split_full(&m, e, WHITESPACE, EXTRACT_RELAX|EXTRACT_UNQUOTE);
                                 if (r < 0) {
                                         ret[k] = NULL;
                                         strv_free(ret);