Remove xclip-mode & osx-clipboard-mode

Due to the varied approaches to terminal environments, I leave it up to
the user to handle restoration of the clipboard.

core/packages.el

@@ -31,13 +31,11 @@
   ;; I've created my own mirror for it because git.savannah.gnu.org runs on a
   ;; potato.
   :recipe (:host github :repo "hlissner/emacs-so-long"))
-(package! osx-clipboard :ignore (not IS-MAC))
 (package! undo-tree
   ;; NOTE The version of undo-tree published to ELPA is over 5 years old and
   ;; missing some fixes. Just use the maintainer's repo directly.
   :recipe (:host nil :repo "http://www.dr-qubit.org/git/undo-tree.git"))
 (package! ws-butler)
-(package! xclip :ignore (not IS-LINUX))
 
 ;; core-projects.el
 (package! projectile)