serializer.helper.ts: fix test for changes to expectedCount

Author: dconeybe

packages/firestore/test/unit/remote/serializer.helper.ts

@@ -1778,8 +1778,7 @@ export function serializerTest(
             }
           },
           resumeToken: new Uint8Array([1, 2, 3]),
-          targetId: 1,
-          expectedCount: undefined
+          targetId: 1
         };
         expect(result).to.deep.equal(expected);
       });