parser: Remove incorrect block-related comment in lily_parser.
Symtab now calculated hashes. Also, a trick for zapping lexer hashes.

The trick is to take a char[8] and cast it as a uint64_t and then set it the
cast to zero. This causes the whole char[8] to be zero-filled, avoiding a
memset call in lexer (and in a very hot part of lexer, no less!)

This was done partly because it kept Lily from being properly compiled by
clang: Somehow the hashes were off, giving 'print has not been declared'
errors.