travis: remove brew update and osxfuse install (#17429)

.travis.yml

@@ -30,8 +30,6 @@ matrix:
       go: 1.10.x
       script:
         - unset -f cd # workaround for https://github.com/travis-ci/travis-ci/issues/8703
-        - brew update
-        - brew cask install osxfuse
         - go run build/ci.go install
         - go run build/ci.go test -coverage $TEST_PACKAGES