unix-abstract consistency: remove __linux__ test

Explicitly disabling 'unix-abstract:' on non-Linux Unix platforms
needs more work than this, but maybe it's not worth it since the
result would just be a different runtime failure message. For now
just be consistent

c++/src/kj/async-io-test.c++

@@ -102,9 +102,7 @@ TEST(AsyncIo, AddressParsing) {
 
 #if !_WIN32
   EXPECT_EQ("unix:foo/bar/baz", tryParse(w, network, "unix:foo/bar/baz"));
-#if __linux__
   EXPECT_EQ("unix-abstract:foo/bar/baz", tryParse(w, network, "unix-abstract:foo/bar/baz"));
-#endif
 #endif
 
   // We can parse services by name...