Tidy neovim configuration

* Remove some unused plugins and packages.
  * e.g. floaterm, projectionist, vim-wiki, vim-easy-align,
    vim-surround, visual-star-search, vim-rhubarb
* Replace none-ls with conform.nvim and nvim-lint.
* Replace lualine.nvim with mini-statusline.
* Add neodev.
* Simplify cmp completion sources.

.luacheckrc

@@ -0,0 +1 @@
+globals = { "vim" }