Remove Firebase xcode project (#4588)

Author: paulb777

.travis.yml

@@ -26,14 +26,6 @@ jobs:
     # The order of builds matters (even though they are run in parallel):
     # Travis will schedule them in the same order they are listed here.
 
-    - stage: test
-      env:
-        - PROJECT=Firebase PLATFORM=iOS METHOD=xcodebuild
-      before_install:
-        - ./scripts/if_changed.sh ./scripts/install_prereqs.sh
-      script:
-        - travis_retry ./scripts/if_changed.sh ./scripts/build.sh $PROJECT $PLATFORM
-
     - stage: test
       env:
         - PROJECT=Core METHOD=pod-lib-lint