Rollup merge of #106714 - Ezrashaw:remove-e0490, r=davidtwco

remove unreachable error code `E0490`

AFAIK, the untested and undocumented error code `E0490` is now unreachable, it was from the days of the original borrow checker.

cc ``@GuillaumeGomez`` #61137

diff --cc compiler/rustc_error_codes/src/error_codes.rs
Simple merge

diff --cc compiler/rustc_infer/src/infer/mod.rs
Simple merge

diff --cc src/tools/tidy/src/error_codes.rs
Simple merge