Do not generate @NotNull annotations on void- or primitive-returning methods

#KT-4834 Fixed
  #KT-5255 Fixed

compiler/testData/asJava/lightClasses/nullabilityAnnotations/OverrideAnyWithUnit.kt

@@ -0,0 +1,9 @@
+// C
+
+trait Base {
+    fun foo(): Any
+}
+
+class C : Base {
+    override fun foo(): Unit {}
+}