testcrate/lib.rs: use #![no_std] unconditionally

testcrate/src/lib.rs

@@ -1,9 +1 @@
-#![cfg_attr(feature = "no_std", no_std)]
-
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}
+#![no_std]