Assume that browser has working URL object (#19283)

Perhaps 10 years ago there was possibility that the URL object didn't
exist, but today we don't support such browsers

See https://caniuse.com/url.

This is a followup to #19277 which did the same for the Blob
constructor.

Author: sbc100

src/library_browser.js

@@ -105,11 +105,6 @@ var LibraryBrowser = {
 
       if (Browser.initted) return;
       Browser.initted = true;
-      Browser.URLObject = typeof window != "undefined" ? (window.URL ? window.URL : window.webkitURL) : undefined;
-      if (!Module.noImageDecoding && typeof Browser.URLObject == 'undefined') {
-        err("warning: Browser does not support creating object URLs. Built-in browser image decoding will not be available.");
-        Module.noImageDecoding = true;
-      }
 
       // Support for plugins that can process preloaded files. You can add more of these to
       // your app by creating and appending to Module.preloadPlugins.
@@ -129,7 +124,7 @@ var LibraryBrowser = {
           // Safari's Blob can only take an ArrayBuffer
           b = new Blob([(new Uint8Array(byteArray)).buffer], { type: Browser.getMimetype(name) });
         }
-        var url = Browser.URLObject.createObjectURL(b);
+        var url = URL.createObjectURL(b);
 #if ASSERTIONS
         assert(typeof url == 'string', 'createObjectURL must return a url as a string');
 #endif
@@ -142,7 +137,7 @@ var LibraryBrowser = {
           var ctx = canvas.getContext('2d');
           ctx.drawImage(img, 0, 0);
           preloadedImages[name] = canvas;
-          Browser.URLObject.revokeObjectURL(url);
+          URL.revokeObjectURL(url);
           if (onload) onload(byteArray);
         };
         img.onerror = (event) => {
@@ -172,7 +167,7 @@ var LibraryBrowser = {
           if (onerror) onerror();
         }
         var b = new Blob([byteArray], { type: Browser.getMimetype(name) });
-        var url = Browser.URLObject.createObjectURL(b); // XXX we never revoke this!
+        var url = URL.createObjectURL(b); // XXX we never revoke this!
 #if ASSERTIONS
         assert(typeof url == 'string', 'createObjectURL must return a url as a string');
 #endif