fix: New Mocha tests.

This removes unstubbing since it can't really work well, anyway, which
fixes the Mocha tests that validate initialization and disposal for the
KeyboardNavigation class.

Author: BenHenning

src/navigation_controller.ts

@@ -303,7 +303,5 @@ export class NavigationController {
     }
     this.removeShortcutHandlers();
     this.navigation.dispose();
-
-    FunctionStubber.getInstance().unstubPrototypes();
   }
 }

src/screenreader/function_stubber_registry.ts

@@ -44,17 +44,6 @@ class Registration<T> {
       return result;
     };
   }
-
-  unstubPrototype(): void {
-    if (this.oldMethod) {
-      throw new Error(
-        `Function is not currently stubbed: ${this.methodNameToOverride}.`,
-      );
-    }
-    const genericPrototype = this.classPrototype as any;
-    genericPrototype[this.methodNameToOverride] = this.oldMethod;
-    this.oldMethod = null;
-  }
 }
 
 export class FunctionStubber {
@@ -104,13 +93,6 @@ export class FunctionStubber {
     this.registrations.forEach((registration) => registration.stubPrototype());
   }
 
-  unstubPrototypes() {
-    this.registrations.forEach((registration) =>
-      registration.unstubPrototype(),
-    );
-    this.isFinalized = false;
-  }
-
   private static instance: FunctionStubber | null = null;
 
   static getInstance(): FunctionStubber {