Revert some changes from 3042a80f

Too many places right now depend on `KotlinClassHeader.data` and
`KotlinClassHeader.strings` being saved even if empty,
and not being null

See KT-39492

core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/header/ReadKotlinClassHeaderAnnotationVisitor.java

@@ -200,9 +200,7 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
             return new CollectStringArrayAnnotationVisitor() {
                 @Override
                 protected void visitEnd(@NotNull String[] result) {
-                    if (result.length > 0) {
-                        data = result;
-                    }
+                    data = result;
                 }
             };
         }
@@ -212,9 +210,7 @@ public class ReadKotlinClassHeaderAnnotationVisitor implements AnnotationVisitor
             return new CollectStringArrayAnnotationVisitor() {
                 @Override
                 protected void visitEnd(@NotNull String[] result) {
-                    if (result.length > 0) {
-                        strings = result;
-                    }
+                    strings = result;
                 }
             };
         }