[compiler][be] Remove unused experimental Rust port

I wrote this a couple summers back as an experiment to see how easily we could translate the compiler to Rust. We make extensive use of in-place mutation of the IR, and the experiment proved that this we can get reasonable ergonomics for this in Rust which was cool. We've since ended up using some of the code here for Relay, allowing Relay Compiler to parse JS files to do more fine-grained extraction of data. For React Compiler though, we plan to continue using JavaScript and explore lightweight native wrappers for things like OXC and SWC plugins. We're also working with the Hermes team to eventually compile the compiler with Static Hermes.

As Tomo always says: always bet on JavaScript.

ghstack-source-id: c5770a2efce16a7153dd98702f47bc84d380c8b2
Pull Request resolved: facebook#32219