tree-sitter: fix lint, delete "demo" plugin (replaced by functional tests)

runtime/plugin/ts_test.vim

@@ -1,32 +0,0 @@
-let g:ts_test_path = expand("<sfile>:p:h:h")
-let g:has_ts = v:false
-
-func! TSTest()
-  if g:has_ts
-    return
-  end
-  " TODO: module!
-  lua theparser = vim.treesitter.create_parser(0)
-  lua require'treesitter_demo'
-  let g:has_ts = v:true
-endfunc
-
-func! TSCursor()
-  " disable matchparen
-  NoMatchParen
-  call TSTest()
-  au CursorMoved <buffer> lua ts_cursor()
-  au CursorMovedI <buffer> lua ts_cursor()
-  map <buffer> <Plug>(ts-expand) <cmd>lua ts_expand_node()<cr>
-endfunc
-
-func! TSSyntax()
-  " disable matchparen
-  set syntax=
-  call TSTest()
-  lua ts_syntax()
-endfunc
-
-command! TSTest call TSTest()
-command! TSCursor call TSCursor()
-command! TSSyntax call TSSyntax()