ci: speed up presubmit downstream test by not explicitly installing all modules in google-cloud-java (#1257)

Author: burkedavison

.kokoro/presubmit/downstream-build.sh

@@ -94,6 +94,5 @@ source ./.kokoro/common.sh
 RETURN_CODE=0
 setup_application_credentials
 setup_cloud "$MODULES_UNDER_TEST"
-install_modules
 run_graalvm_tests "$MODULES_UNDER_TEST"
 exit $RETURN_CODE