With the current patch, pass will try to use `xclip` when `$DISPLAY` is
set. Termux (most of the time) doesn't have `xclip` even if `$DISPLAY`
is set, so this change will check for `xclip` specifically (and
`wl-copy`/`wl-paste` in case of `$WAYLAND_DISPLAY`).
So, if a user has `xclip` and `$DISPLAY` set, it will still use `xclip`,
otherwise it will use `termux-clipboard-set`.
Since 5b3f31bf14 fixes the newline being added to termux-clipboard-get, this workaround is no longer required here and actually breaks the comparission.
