title: implicit definition of token in parser warning, when definition in lexer
body: <p>I get this warning when trying to build the parser using version ANTLR 4.7.2</p>
  <pre><code>warning(125): CobolParser.g4:1075:20: implicit definition of token END_ACCEPT in parser
  </code></pre>
  <p>If I change the accept_statement rule to use END_ADD instead of END_ACCEPT,
  the parser builds without warnings.</p>
  <p>Would you please explain why I am getting this warning,
  since the END_ACCEPT is defined in the lexer?</p>
  <p>From CobolLexer.g4:</p>
  <pre><code>END:                 [Ee][Nn][Dd] ;
  END_ACCEPT:          END '-' [Aa][Cc][Cc][Ee][Pp][Tt] ;
  END_ADD:             END '-' [Aa][Dd][Dd] ;
  </code></pre>
  <p>From CobolParser.g4:</p>
  <pre><code>options { tokenVocab=CobolLexer; }
  
  accept_statement:   ACCEPT accept_target 
                      from_clause? 
                      on_exception_clause* 
                      END_ACCEPT?;
  
  simple_add:         ADD add_from+ 
                      (TO     add_to+)? 
                      (GIVING add_giving+)? 
                      on_size_error_clause*
                      END_ADD?;
  </code></pre>