Remove workaround for neovim's broken GUI detection

It looks like finally neovim got sane GUI detection support, like vim
[0].
This means we can remove the temporary workaround from 95a6ccb
completely.

Nightly neovim users who used a version of neovim released after
the broken 2022-12-01 version [1], but before the fix in 2023-02-28,
should update their version of neovim as soon as possible, as the root
of the problem is now properly fixed for neovim 0.9.

Fixes #46.

[0] neovim/neovim#22382
[1] neovim/neovim#18375

autoload/tpipeline/util.vim

@@ -16,7 +16,7 @@ func tpipeline#util#set_size()
 endfunc
 
 func tpipeline#util#check_gui()
-	if (v:event['chan'] && !(has('nvim-0.9') && nvim_list_uis()[0].ext_termcolors)) || has('gui_running')
+	if (v:event['chan'] && !has('nvim-0.9')) || has('gui_running')
 		call tpipeline#state#restore()
 	endif
 endfunc