[IR] Don't produce gaps for skipped IR declarations during serialization

compiler/util-klib/src/org/jetbrains/kotlin/library/KotlinLibraryWriter.kt

@@ -32,24 +32,8 @@ class SerializedMetadata(
     val fragmentNames: List<String>
 )
 
-sealed class SerializedDeclaration {
-    abstract val id: Int
-    abstract val size: Int
-    abstract val bytes: ByteArray
-
-    abstract val declarationName: String
-}
-
-class TopLevelDeclaration(override val id: Int, override val declarationName: String, override val bytes: ByteArray) :
-    SerializedDeclaration() {
-    override val size = bytes.size
-}
-
-object SkippedDeclaration : SerializedDeclaration() {
-    override val id = -1
-    override val size = 0
-    override val bytes = ByteArray(0)
-    override val declarationName: String = "<SKIPPED>"
+class SerializedDeclaration(val id: Int, val declarationName: String, val bytes: ByteArray) {
+    val size = bytes.size
 }
 
 class SerializedIrFile(