firebase-ios-sdk

Enable code coverage for AllUnitTests_iOS target (#2450)

* Enable code coverage for `AllUnitTests_iOS`

* FIRAuthAppDelegateProxyTests: fix for test of a delegate with no implemented methods.

Issue:
After deallocating of the proxy [delegate application:_mockApplication openURL:_url options:@{}] starts returning either YES or NO.
The issue is reproducible only when Code Coverage is enabled for AllUnitTests_iOS target.
Possible reason:
-[FIRAuthAppDelegateProxy dealloc] replaces implementation of the methods that were not implemented in the original delegate by `noop` function that doesn't have a return value.
Fix:
Ignore return value in the tests. The case is unlikely to happen in a real application.

* Code formatting