remote: print an error if refspec cannot be removed

If the existing fetch refspecs cannot be removed when replacing the set
of branches to fetch with "git remote set-branches" the command silently
fails. Add an error message to tell the user what when wrong.

Signed-off-by: Phillip Wood <[email protected]>

Author: phillipwood

builtin/remote.c

@@ -1603,6 +1603,7 @@ static int set_remote_branches(const char *remotename, const char **branches,
 	}
 
 	if (!add_mode && remove_all_fetch_refspecs(key.buf)) {
+		error(_("could not remove existing fetch refspec"));
 		strbuf_release(&key);
 		return 1;
 	}