Revert "ci: Freeze rustc for nightly web builds to 1.81.0"

[torokati44]

Reverts #18397.

To be merged once rustwasm/wasm-bindgen#4213 is merged and released, so rustwasm/wasm-bindgen#4227 can be fixed properly.

Also referencing rustwasm/wasm-bindgen#4211.

[danielhjacobs]

Referencing #18528

[danielhjacobs]

Two options for merging this PR:

1. Merge web: Allow building an MVP vanilla WASM module #18528, integrate it into CI with these commands: web: Allow building an MVP vanilla WASM module #18528 (comment), and then merge this, therefore supporting all the browsers we currently support.
2. Accept the loss of Pale Moon support, Basilisk support, and Safari 14.1 as acceptable, announce it, note it on https://github.com/ruffle-rs/ruffle/wiki#web, merge web: Throw an error when reference types are unsupported #18838, and then merge this, therefore adding a message that browsers without reference-types are unsupported.