Configure cmake-language-server and coc-cmake

Utilises the following Python package:

```console
$ pip3 install --user cmake-language-server
```

after/ftplugin/cmake.vim

@@ -1,6 +1,3 @@
-" Add omnifunc completion plugin.
-packadd vim-cmake-completion
-
 " Enable syntax folding, see .vim/after/syntax/cmake.vim
 setlocal foldmethod=syntax
 " Set comment string

autoload/build.vim

@@ -40,6 +40,7 @@ function! build#dir(...) abort
     " TODO: Check .vim/coc-settings.json exists, create it if not
     let l:coc_settings = json_decode(join(readfile('.vim/coc-settings.json'), ''))
     let l:coc_settings['clangd.compilationDatabasePath'] = $BUILD_DIR
+    let l:coc_settings['cmake.lsp.buildDirectory'] = $BUILD_DIR
     call writefile([json_encode(l:coc_settings)], '.vim/coc-settings.json')
     CocRestart
   endif

coc-settings.json

@@ -0,0 +1 @@
+{"cmake.lsp.enable": true}

vimrc

@@ -40,8 +40,6 @@ Pack 'neoclide/coc.nvim', {'branch': 'release'}
 " ultisnips - snippet engine
 Pack 'SirVer/ultisnips'
 Pack 'honza/vim-snippets'
-" vim-cmake-completion - completion & help
-Pack 'kbenzie/vim-cmake-completion', {'type': 'opt'}
 " vimomni - Completion for vimscript
 Pack 'vim-scripts/vimomni', {'type': 'opt'}