use coder/websocket for everything, get rid of gobwas.

supposedly it is faster, and anyway it's better to use it since we're already using it for wasm/js.

(previously named nhooyr/websocket).

README.md

@@ -150,7 +150,7 @@ To use it, use `-tags=libsecp256k1` whenever you're compiling your program that
 Install [wasmbrowsertest](https://github.com/agnivade/wasmbrowsertest), then run tests:
 
 ```sh
-TEST_RELAY_URL=<relay_url> GOOS=js GOARCH=wasm go test -short ./...
+GOOS=js GOARCH=wasm go test -short ./...
 ```
 
 ## Warning: risk of goroutine bloat (if used incorrectly)