fix: remove redundant UIEnter subscription

[crackcomm]

The UIEnter event is not needed for setting up the highlight groups in cmp.lua.

This caused a bug displaying ANSI escape sequences in neovim in tmux, kitty, and alacritty.

I found this bug after 2 days of debugging, searching for the cause in the wrong place - zsh, tmux, kitty, then testing on alacritty and xterm, and finally realizing that the issue was in the Neovim configuration itself.

If this does not in fact fix the issue, even though I tested it thoroughly, it is still a redundant call in my opinion, especially since ColorScheme event is immediately triggered after the subscription.

[crackcomm]

I notice that it is a fix for #1649, maybe it's appropriate to keep this functionality for vim.fn.has('headless') == 1 - I'm not sure.

[wsdjeg]

neovim supports has('headless')?

maybe you can check v:argv, use if vim.tbl_contains(vim.v.argv, '--headless') then end