Don't introduce @NotNull on Kotlin methods that already have that annotation

This usually can't happen, but delegates pointing at Java appear to be synthesised with this normally-hidden annotation

java/ql/integration-tests/all-platforms/kotlin/nullability-annotations/AnnotatedMethods.java

@@ -1,7 +1,7 @@
 import org.jetbrains.annotations.*;
 import zpkg.A;
 
-public class AnnotatedMethods {
+public class AnnotatedMethods implements AnnotatedInterface {
 
   public @A @NotNull String notNullAnnotated(@A @NotNull String param) { return param; }