(PUP-3274)(PUP-3638) Make future parser standard and remove 3x parser/lexer/ast

This is a mega removal and cleanup of old 3x code.

* Removal of lexer, parser, and the majority of the AST classes (except those still used by the compiler
* Removal of related tests; merging future and old tests that should remain
* Removal of parser setting
* Removal of binder setting
* Cleanup of remaining AST classes
* Adjusting documentation since "future" is now here
* Fixing benchmarks that were specific for future parser
* (PUP-3638) Removal of RDoc1
* (PUP-3638) Removal of RDoc2 generation of documentation for all .pp
* Removal of doc support in the remaining AST classes
I think it should go away. I was on the fence about this; thinking that people looking at 4.0 may want to know if they can use it with future parser in 3x, but then I realized that they should look at the 3x documentation where it provides these details.