Auto merge of #49313 - sgrif:sg-revert-stuff, r=nikomatsakis

Remove universes from `ty::ParamEnv`

This change was never meant to land. #48407 takes an alternate approach. However, that PR is now blocked on some issues with canonicalization, and rebasing these reverts gets harder each time, so let's just get this bit out of the way now.

r? @nikomatsakis

diff --cc src/librustc/infer/canonical.rs
Simple merge

diff --cc src/librustc/traits/error_reporting.rs
Simple merge

diff --cc src/librustc/traits/mod.rs
Simple merge

diff --cc src/librustc/traits/select.rs
Simple merge

diff --cc src/librustc/traits/specialize/mod.rs
Simple merge

diff --cc src/librustc/ty/mod.rs
Simple merge

diff --cc src/librustc/ty/structural_impls.rs
Simple merge

diff --cc src/librustc/ty/sty.rs
Simple merge

diff --cc src/librustc/util/ppaux.rs
Simple merge

diff --cc src/librustc_typeck/check/_match.rs
Simple merge

diff --cc src/librustc_typeck/check/dropck.rs
Simple merge

diff --cc src/librustc_typeck/check/method/mod.rs
Simple merge

diff --cc src/librustc_typeck/check/method/probe.rs
Simple merge

diff --cc src/librustc_typeck/check/method/suggest.rs
Simple merge

diff --cc src/librustc_typeck/check/mod.rs
Simple merge