public void removeLastChild() {
		if ( children!=null ) {
			children.remove(children.size()-1);
		}
	}
Used by enterOuterAlt to toss out a RuleContext previously added as
 we entered a rule. If we have # label, we will need to remove
 generic ruleContext object.
runtime/Java/src/org/antlr/v4/runtime/ParserRuleContext.java