Changed extension in parsing test data (jet -> kt)

compiler/testData/psi/examples/collections/IMutableIterator.kt

@@ -0,0 +1,13 @@
+open class IMutableIterator<out T> : IIterator<T> {
+  fun remove() : T
+
+/*
+  Considerations:
+    pro: why not + non iteration breaking
+    con: counter-intuitive for, e.g., TreeSet
+
+
+  fun addBefore(item : T) : Boolean
+  fun addAfter(item : T) : Boolean
+*/
+}