Remove ObjC tests that check golden generated code

[liamappelbe]

These goldens can only be regenerated on a mac machine, so they make it difficult for people who don't own a mac to contribute. They're also a bit of a nuisance to merge, and we now have good enough coverage with our native_objc_tests that they're not really necessary anymore. The bindings are now generated by native_objc_test/setup.dart, at the same time as the dylibs, and are gitignored.

The objc header_parser tests were removed:

• objc_interface_test was redundant
• objc_basic_types has been merged into native_objc_test/native_objc_test
• objc_config_test was mostly redundant, except for renaming, which has a dedicated test now, called native_objc_test/rename_test

Fixes dart-lang/native#278

[brianquinlan]

Maybe @dcharkes will have an opinion about this?

[dcharkes]

As mentioned in the issue. I think having goldens in general serves a good purpose (and makes reviewing PRs easier when single features are added/tweaked). However, we also want people without Macs to be able to contribute, so removing the goldens for ObjectiveC seems good to me.