internal: Remove TraitEnvironment

[ChayimFriedman2]

We don't need it anymore; ParamEnv is enough.

A lot of code relied on getting the crate from the TraitEnvironment. Some had it readily available from other sources, some changed to take a new struct ParamEnvAndCrate.

I believe some of the code that used to take a TraitEnvironment, now taking ParamEnvAndCrate, e.g. layout and mir eval, only needs the crate - but I'm not entirely sure and this is not for this PR.

[flodiebold]

I believe some of the code that used to take a TraitEnvironment, now taking ParamEnvAndCrate, e.g. layout and mir eval, only needs the crate - but I'm not entirely sure and this is not for this PR.

It has seemed weird to me that layout takes an env, yeah. OTOH rustc's layout query also takes one 🤔

[flodiebold]

It looks to me like layout mostly gets called with an empty env after monomorphization in rustc, but there might be some places that call it before monorphization to e.g. see whether something is a ZST 🤔

[flodiebold]

Looking at our MIR evaluation, I don't think it ever actually gets called with a not-None environment 🤔

• the only place that passes Some env to interpret_mir is const_eval_query
• the only place that calls const_eval with a not-None env is in turn MIR eval.