Revert "Panic if the grammar verifier sees a token it doesn't recognize"

This reverts commit 9c7d5ae57c.

This was wrong... the `continue` was to ignore the latter half of the
tokens file. Another mechanism will have to be used to keep the model
grammar's tokens in sync with the actual grammar's tokens :-/

src/grammar/verify.rs

@@ -111,7 +111,7 @@ fn parse_token_list(file: &str) -> HashMap<String, token::Token> {
             "LIT_BINARY_RAW"    => token::Literal(token::BinaryRaw(Name(0), 0), None),
             "QUESTION"          => token::Question,
             "SHEBANG"           => token::Shebang(Name(0)),
-            _                   => panic!("Bad token str `{}`", val),
+            _                   => continue,
         };
 
         res.insert(num.to_string(), tok);