Update a test

Author: DougGregor

test/decl/class/actor/basic.swift

@@ -7,7 +7,6 @@ actor MyActor { }
 class MyActorSubclass1: MyActor { }
 // expected-error@-1{{actor types do not support inheritance}}
 // expected-error@-2{{type 'MyActorSubclass1' cannot conform to the 'Actor' protocol}}
-// expected-error@-3{{non-final class 'MyActorSubclass1' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
 
 actor MyActorSubclass2: MyActor { } // expected-error{{actor types do not support inheritance}}