This code used to be necessary because of the error messages generated
by the YACC-based parser, but they're no longer relevant under the new
recursive descent parser:
- LBRACE no longer exists, so "{ or {" can never occur.
- The parser never generates error messages about "@" or "?" now
(except in import sections, where they're actually legitimate).
- The s/LLITERAL/litbuf/ substitution is handled in p.syntax_error.