remove modified Pathname#write monkeypatch

from homebrew-fork.  It appears we do not depend on this behavior.
remove modified Pathname#extname monkeypatch

from homebrew-fork.  It appears we do not depend on this behavior.
rm unused homebrew-fork extend/pathname methods

* stem
* text_executable?
adopt homebrew-fork Ruby 2.0.0 Pathname encode fix

into our main codebase per https://bugs.ruby-lang.org/issues/9915
remove Pathname#cd monkeypatch

from homebrew-fork.  Replace our single use of this method in doctor.rb
Merge pull request #8403 from rolandwalker/strip_homebrew_extend_pathname

Strip homebrew-fork `extend/pathname.rb`