[nvim] Update vim-slime configuration.

.vimrc

@@ -112,14 +112,11 @@ call plug#end()
 
 " vim-slime settings for use in tmux
 :let g:slime_target="tmux"
-:let g:slime_default_config={"socket_name": "default", "target_pane": "{last}"}
-:let g:slime_dont_ask_default=1
 :function SlimeOverrideConfig()
 :    " This expands {last} to a fixed pane id. This is done in the override function in
 :    " order to delay the expansion until first usage instead of when Vim starts.
-:    let b:slime_config = g:slime_default_config
 :    let l:last_pane_id = trim(system('tmux display -pt "{last}" "#{pane_id}"'))
-:    let b:slime_config['target_pane'] = l:last_pane_id
+:    let b:slime_config = {"socket_name": "default", "target_pane": l:last_pane_id}
 :endfunction
 :let g:slime_bracketed_paste=1
 :nnoremap <C-c><C-c> <Plug>SlimeParagraphSend