Don't install the Cloud SDK on Travis

We don't need this anymore.

travis/setup.sh

 #!/bin/bash
-set -e
-
-if [ $TRAVIS_PULL_REQUEST = "false" ]; then
-  echo $KEY_FILE | base64 --decode > gcloud_key_file.json
-fi
-
-set -x
+set -ex
 
 # Download dependencies flutter
 ./bin/flutter --version
 ./bin/flutter update-packages
-
-if [ $TRAVIS_PULL_REQUEST = "false" ]; then
-  export CLOUDSDK_CORE_DISABLE_PROMPTS=1
-  curl https://sdk.cloud.google.com | bash
-fi