delete canvas2D map canvas — WebGL is the only renderer left

After every map-anchored visual moved to WebGL (terrain, territory,
structures, names, selection boxes, ghost preview, move chevrons,
FX) there's nothing drawing to the canvas2D context. Rip it out.

src/client/InputHandler.ts

@@ -246,7 +246,7 @@ export class InputHandler {
   constructor(
     private gameView: GameView,
     public uiState: UIState,
-    private canvas: HTMLCanvasElement,
+    private canvas: HTMLElement,
     private eventBus: EventBus,
   ) {}