Rollup merge of #58476 - nnethercote:rm-LazyTokenStream, r=petrochenkov

Remove `LazyTokenStream`.

`LazyTokenStream` was added in #40939. Perhaps it was an effective optimization then, but no longer. This PR removes it, making the code both simpler and faster.

r? @alexcrichton

diff --cc src/librustc/hir/lowering.rs
Simple merge

diff --cc src/libsyntax/ext/expand.rs
Simple merge

diff --cc src/libsyntax/mut_visit.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
Simple merge