Remove the ability to pass in more than one font to BaseFontLoader.bind

- The only existing call-site, of this method, is never passing more than *one* font at a time anyway.
 - As far as I can remember, this functionality has never actually been used (caveat: I didn't check the git history).
 - This allows simplification of the method, especially by making use of the fact that it's now asynchronous.
 - It should be just as easy to call `BaseFontLoader.bind` from within a loop, rather than having the loop in the method itself.

src/display/api.js

@@ -1945,7 +1945,7 @@ class WorkerTransport {
             fontRegistry,
           });
 
-          this.fontLoader.bind([font]).then(() => {
+          this.fontLoader.bind(font).then(() => {
             this.commonObjs.resolve(id, font);
           });
           break;