Update error message for uid field.

Author: yuchenshi

packages/util/src/emulator.ts

@@ -99,7 +99,7 @@ export function createMockUserToken(
 ): string {
   if (token.uid) {
     throw new Error(
-      'Invalid mockUserToken field "uid". Did you mean "sub" (for Firebase Auth User ID)?'
+      'The "uid" field is no longer supported by mockUserToken. Please use "sub" instead for Firebase Auth User ID.'
     );
   }
   // Unsecured JWTs use "none" as the algorithm.

packages/util/test/emulator.test.ts

@@ -52,7 +52,7 @@ describe('createMockUserToken()', () => {
     expect(() =>
       createMockUserToken((options as unknown) as EmulatorMockTokenOptions)
     ).to.throw(
-      'Invalid mockUserToken field "uid". Did you mean "sub" (for Firebase Auth User ID)?'
+      'The "uid" field is no longer supported by mockUserToken. Please use "sub" instead for Firebase Auth User ID.'
     );
   });
 });