Remove unnecessary steps from Travis build

.travis.yml

@@ -36,12 +36,9 @@ before_install:
   - echo ls_ruby_bindir; ls "/System/Library/Frameworks/Ruby.framework/Versions/${CASK_RUBY_TEST_VERSION}/usr/bin"
 
 # install steps
-# * brew Formulae without which some tests will be skipped
 # * bundler gem
 # * Ruby gems required for brew-cask
 install:
-  - brew install cabextract
-  - brew install unar
   - echo gem_install_bundler; sudo "/System/Library/Frameworks/Ruby.framework/Versions/${CASK_RUBY_TEST_VERSION}/usr/bin/gem" install bundler --bindir="/System/Library/Frameworks/Ruby.framework/Versions/${CASK_RUBY_TEST_VERSION}/usr/bin"
   - echo bundle; sudo "/System/Library/Frameworks/Ruby.framework/Versions/${CASK_RUBY_TEST_VERSION}/usr/bin/bundle" --system
   - brew install caskroom/cask/brew-cask