Removed manually cloned emacs-powerline.
Squashed 'vendor/emacs-powerline/' content from commit 1a57009

git-subtree-dir: vendor/emacs-powerline
git-subtree-split: 1a570099a814ea17f151cca7ad44334741b85371
Merge commit '42b94f715752a334ea7637f1d227581dcd6f3d86' as 'vendor/emacs-powerline'