* Migrate Firebase off @import statements
* - Migrate tests and test utils from @import to #import.
- Update Xcode projects for tests to explicitly link in framework deps.
- Update check_no_module_imports.sh to look for @imports in tests/test utils/
integration tests.
* Ensure check_no_module_imports.sh explicitly exits with code 0 on success.
* Remove mostly unused code from FIRMessagingLogger
This cleans up some left-over old logging logic from before we moved to FIRLogger in Firebase Core. We no longer need this logging functionality.
* Delete FIRMessagingConfig.{h,m}
We no longer need a config class to store an unused log level filter (that filter is no longer needed).
Chen Liang