feat(lsp): deprecate execute_command with client:exec_cmd

runtime/lua/vim/lsp/completion.lua

@@ -548,15 +548,7 @@ local function on_complete_done()
 
     local command = completion_item.command
     if command then
-      client:_exec_cmd(command, { bufnr = bufnr }, nil, function()
-        vim.lsp.log.warn(
-          string.format(
-            'Language server `%s` does not support command `%s`. This command may require a client extension.',
-            client.name,
-            command.command
-          )
-        )
-      end)
+      client:exec_cmd(command, { bufnr = bufnr })
     end
   end