Dedup buffer entries on remote tmux session (currently 3 copies are generated)

[ibhagwan]

The current situation on remote tmux:

• Neovim detects tmux as it's clipboard (vs xclip, xsel, etc) thus when smaryank sets the + register, the 1st buffer is generated
• Then comes the tmux set-buffer, 2nd copy
• OSC52 sequence generates yet another copy in the remote tmux so we end up with 3 copies of the same yank