[MySql] Removed outdated comment (#2660)
[MySql] Removed outdated comment (#2660)

The comment about using a custom character stream is no longer needed after the addition of `options { caseInsensitive = true; }` to the lexer grammar in https://github.com/antlr/grammars-v4/commit/c810ec33085922e2138efd1b3268c481997f9573#diff-1cb407f308a0912bae7df6e93484f4592fbfdc65ae8e52fa1fc49a5d28e8d700
antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4,antlr/grammars-v4