Cleanup: remove .travis.yml since it is unused (#32494)

AFAICT, travis hasn't been disabled for the grpc/grpc repository a long
time ago.
https://travis-ci.org/github/grpc/grpc
https://travis-ci.com/github/grpc/grpc

I'm happy to be proven wrong if travis is still being used, but if not,
we should delete the travis config to avoid confusing people (I've seen
some recently open PRs attempting to make modification to this file).

.travis.yml

@@ -1,69 +0,0 @@
-git:
-  depth: 1
-language: objective-c
-osx_image: xcode7.3
-env:
-  global:
-    - CONFIG=opt
-    - TEST=objc
-    - JOBS=1
-  matrix:
-    - SCHEME="RxLibraryUnitTests"
-      WORKSPACE="Tests.xcworkspace" TEST_PATH="src/objective-c/tests" BUILD_ONLY="false"
-      INTEROP_SERVER="false"
-    - SCHEME="InteropTestsLocalSSL"
-      WORKSPACE="Tests.xcworkspace" TEST_PATH="src/objective-c/tests" BUILD_ONLY="false"
-      INTEROP_SERVER="true"
-    - SCHEME="InteropTestsLocalCleartext"
-      WORKSPACE="Tests.xcworkspace" TEST_PATH="src/objective-c/tests"  BUILD_ONLY="false"
-      INTEROP_SERVER="true"
-    # TODO(jcanizales): Make tests an app project (instead of library), so the following will work.
-    # - SCHEME="InteropTestsRemote"
-    #   WORKSPACE="Tests.xcworkspace" TEST_PATH="src/objective-c/tests" BUILD_ONLY="false"
-    #   INTEROP_SERVER="true"
-    - SCHEME="HelloWorld"
-      WORKSPACE="HelloWorld.xcworkspace" TEST_PATH="examples/objective-c/helloworld"
-      BUILD_ONLY="true" INTEROP_SERVER="false"
-    - SCHEME="RouteGuideClient"
-      WORKSPACE="RouteGuideClient.xcworkspace" TEST_PATH="examples/objective-c/route_guide"
-      BUILD_ONLY="true" INTEROP_SERVER="false"
-    - SCHEME="AuthSample"
-      WORKSPACE="AuthSample.xcworkspace" TEST_PATH="examples/objective-c/auth_sample"
-      BUILD_ONLY="true" INTEROP_SERVER="false"
-    - SCHEME="Sample"
-      WORKSPACE="Sample.xcworkspace" TEST_PATH="src/objective-c/examples/Sample" BUILD_ONLY="true"
-      INTEROP_SERVER="false"
-    - SCHEME="Sample"
-      WORKSPACE="Sample.xcworkspace" TEST_PATH="src/objective-c/examples/Sample" BUILD_ONLY="true"
-      INTEROP_SERVER="false" FRAMEWORKS="YES"
-    - SCHEME="SwiftSample"
-      WORKSPACE="SwiftSample.xcworkspace" TEST_PATH="src/objective-c/examples/SwiftSample"
-      BUILD_ONLY="true" INTEROP_SERVER="false"
-before_install:
-  # Until Travis upgrades from Cocoapods 0.39, we need to do it here.
-  - pod --version
-  - gem uninstall cocoapods -a
-  - gem install cocoapods -v '1.0.1'
-  - pod --version
-  # Recent pods aren't found if we don't explicitly update Cocoapods' repo.
-  - pod repo update
-install:
-  - pushd $TEST_PATH
-  - pod install
-  - popd
-before_script:
-  - if [ "${INTEROP_SERVER}" = "true" ]; then
-      make interop_server;
-      (bins/$CONFIG/interop_server --port=5050 &);
-      (bins/$CONFIG/interop_server --port=5051 --use_tls &);
-    fi
-script:
-  - if [ "${BUILD_ONLY}" = "true" ]; then
-      xctool -workspace "$TEST_PATH/$WORKSPACE" -scheme "$SCHEME"
-      -sdk iphonesimulator9.3 build;
-    else
-      xctool -workspace "$TEST_PATH/$WORKSPACE" -scheme "$SCHEME"
-      -sdk iphonesimulator9.3 test;
-    fi
-notifications:
-  email: false