drop osx and clang because they are often fails and slow
	* .travis.yml: removed osx code. follow up with r53517

	* .travis.yml: removed commented-out code.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@54356 b2dd03c8-39d4-4d8f-98ff-823fe69b080e