A minor style fix (a possible memory usage improvement)

lark/parsers/grammar_analysis.py

@@ -136,7 +136,8 @@ class GrammarAnalyzer(object):
                     if not is_terminal(new_r):
                         yield new_r
 
-        _ = list(bfs([rule], _expand_rule))
+        for _ in bfs([rule], _expand_rule):
+            pass
 
         return fzset(init_ptrs)