getrandom's "js" feature should not be enabled in libraries

[japaric]

getrandom's docs state:

This feature should only be enabled for binary, test, or benchmark crates. Library crates should generally not enable this feature, leaving such a decision to users of their library. Also, libraries should not introduce their own js features just to enable getrandom’s js feature.

currently the hpke-rs-crypto, hpke-rs-evercrypt and hpke-rs-rust-crypto libraries are enabling the "js" feature. if the feature is desired to, for example, run benchmarks on wasm32-unknown-unknown then the getrandom dependency should be moved under the dev-dependecies section so that only benchmark binaries see it.

[franziskuskiefer]

Indeed. This was laziness on my side and it didn't hurt so far. I'd be fine with removing it.