Remove unnecessary grammars and generated files from repository

[EvanKirshenbaum]

In addition to the DMF (soon to be DML (#261)) grammar and its associated lexer grammar, there are two vestigial grammars sitting in mpam/grammar: firstPathTry.g4 and simple.g4. These came from earlier experiments in creating what would become the current macro language, and the files (and, especially, the generated files in target/generated-sources/antlr4) are just going to confuse people. They should be removed.

Migrated from internal repository. Originally created by @EvanKirshenbaum on Mar 29, 2023 at 11:05 AM PDT. Closed on Aug 14, 2023 at 12:49 PM PDT.

[EvanKirshenbaum]

This issue was referenced by the following commit before migration:

• 3bd70f64517e13f36873518c7d9a0155008efadc by @EvanKirshenbaum on Aug 14, 2023 at 11:54 AM PDT