Remove pointless Display.clear()

It served no meaningful purpose and it had bugs. So let's remove it
rather than try to fix it.

core/display.js

@@ -60,8 +60,6 @@ export default class Display {
 
         Log.Debug("User Agent: " + navigator.userAgent);
 
-        this.clear();
-
         // Check canvas features
         if (!('createImageData' in this._drawCtx)) {
             throw new Error("Canvas does not support createImageData");
@@ -301,12 +299,6 @@ export default class Display {
         }
     }
 
-    clear() {
-        this.resize(240, 20);
-        this._drawCtx.clearRect(0, 0, this._fb_width, this._fb_height);
-        this.flip();
-    }
-
     pending() {
         return this._renderQ.length > 0;
     }

core/rfb.js

@@ -172,7 +172,6 @@ export default class RFB extends EventTargetMixin {
             throw exc;
         }
         this._display.onflush = this._onFlush.bind(this);
-        this._display.clear();
 
         this._keyboard = new Keyboard(this._canvas);
         this._keyboard.onkeyevent = this._handleKeyEvent.bind(this);