Revert "Make pbcopy and pbpaste work in tmux"

This reverts commit 526af342de4c3f69612513a416db3f25fb3ec02c.
Revert "Add alias for pbcopy and pbpaste"

This reverts commit e785c9f56802d8c2c6339dcba96b08e7e81ffac2.
Use alias to fix tmux pbcopy/pbpaste issue

As set option in tmux.conf will mess up in Linux,
turn to use alias like:

`alias pbcopy='reattach-to-user-namespace pbcopy'`