Some random fixes (#2936)

- Do not disable `std` feature in the integration tests
- `contracts-fixtures` test should only check for `riscv` build when the
feature is enabled

substrate/frame/contracts/fixtures/src/lib.rs

@@ -70,6 +70,7 @@ mod test {
 	fn out_dir_should_have_compiled_mocks() {
 		let out_dir: std::path::PathBuf = env!("OUT_DIR").into();
 		assert!(out_dir.join("dummy.wasm").exists());
+		#[cfg(feature = "riscv")]
 		assert!(out_dir.join("dummy.polkavm").exists());
 	}
 }