Go into the options menu, choose “Edit keymaps”, then “Create a keymap”. Press Enter at the “Key” prompt and a single space as the “Action”.
And then you’ll probably want to choose to “Append keymaps to a file” so that it persists for next time you load the game.
This just replaces the default action of Enter with a “do nothing but don’t tell me about help” action. If you want to keep the menu available, say on the ‘Tab’ key, you can also remap the Tab keypress to the \n action.