Remove wasm32-unknown-unknown from build checks

By default `getrandom` 0.2 does not compile on unsupported targets; it
is necessary to enable its `js` feature flag specifically when targeting
`wasm32-unknown-unknown`. Since we don't expose that flag ourselves
(instead relying on the downstream user to do this) we can't directly
test this ourselves. `wasm32-wasi` is fully-supported, so we continue to
test builds against that target to ensure we retain WASM compatibility.

.github/workflows/ci.yml

@@ -49,7 +49,6 @@ jobs:
     strategy:
       matrix:
         target:
-          - wasm32-unknown-unknown
           - wasm32-wasi
 
     steps: