Update literal suffix docs for rust-lang/rust#102944

[mattheww]

rust-lang/rust#102944 has changed how literals with suffixes are dealt with.

Previously, unknown suffixes were rejected by the parser. Now they are accepted by the parser and rejected at a later stage.

I think this means all the business about 'Number pseudoliterals' can disappear from tokens.md.

There are new tests in src/test/ui/lexer/error-stage.rs.

[mattheww]

@rustbot claim
@rustbot label +A-lexer +A-grammar +A-expressions