Delete closure/closure-compiler directory to make way for updated version.

The current version is frozen in time when the Closure Compiler switched
from SVN to Git. We need to delete this version so we can manage it with
git-subtree going forward.
Squashed 'closure/closure-compiler/' content from commit ce86cc8

git-subtree-dir: closure/closure-compiler
git-subtree-split: ce86cc8e460060e1280f365f22ccd5c375e2f5ed
Merge commit 'a97d64b7a64bd8a6ac0a364f671423a32094da7c' as 'closure/closure-compiler'
Added BUCK files back on top of Closure Compiler.
Fix plovr after new closure-compiler import so it compiles.
Squashed 'closure/closure-stylesheets/' content from commit 86bb800

git-subtree-dir: closure/closure-stylesheets
git-subtree-split: 86bb800d79a32bfc0328bbf74bfeb772c6eb73b0
Merge commit '406abdf0687b8b0baac1e15d6fe7091b9de3ca37' as 'closure/closure-stylesheets'