Remove plain wasm32-unknown-unknown build from CI

Author: josephlr

.travis.yml

@@ -50,7 +50,6 @@ matrix:
         #- cargo web test --nodejs --target wasm32-unknown-emscripten
         #- cargo build --target wasm32-unknown-unknown # without any features
         - cargo build --target wasm32-wasi
-        - cargo build --target wasm32-unknown-unknown
         - cargo build --target wasm32-unknown-unknown --features=wasm-bindgen
         - cargo web test --target wasm32-unknown-unknown --features=stdweb
         - cargo build --manifest-path tests/wasm_bindgen/Cargo.toml --target wasm32-unknown-unknown