Remove unused remaps and add coc-rename remap

nvim/coc.vim

@@ -8,8 +8,6 @@ else
 endif
 
 " Use tab for trigger completion with characters ahead and navigate.
-" NOTE: Use command ':verbose imap <tab>' to make sure tab is not mapped by
-" other plugin before putting this into your config.
 inoremap <silent><expr> <TAB>
       \ pumvisible() ? "\<C-n>" :
       \ <SID>check_back_space() ? "\<TAB>" :
@@ -34,11 +32,8 @@ nmap <silent> gd <Plug>(coc-definition)
 " Use <C-l> for trigger snippet expand.
 imap <C-l> <Plug>(coc-snippets-expand)
 
-" Use <C-j> for jump to next placeholder, it's default of coc.nvim
-let g:coc_snippet_next = '<c-j>'
-
-" Use <C-k> for jump to previous placeholder, it's default of coc.nvim
-let g:coc_snippet_prev = '<c-k>'
+" Use F2 to rename a variable, e.g.
+nmap <F2> <Plug>(coc-rename)
 
 let g:coc_global_extensions = [
   \ 'coc-tsserver',