Revert temporary type adjustments on builtins

These were made during migration of builtins from package "jet" to "kotlin"

core/builtins/native/kotlin/Array.kt

@@ -16,7 +16,7 @@
 
 package kotlin
 
-public class Array<reified T>(public val size: Int, init: Function1<Int, T>) {
+public class Array<reified T>(public val size: Int, init: (Int) -> T) {
     public fun get(index: Int): T
     public fun set(index: Int, value: T): Unit
 

core/builtins/src/kotlin/Unit.kt

@@ -17,7 +17,7 @@
 package kotlin
 
 public class Unit private() {
-    override fun toString(): String = "Unit.VALUE"
+    override fun toString() = "Unit.VALUE"
 
     class object {
         public val VALUE: Unit = Unit()