Migrate testdata to new lambda syntax

compiler/testData/codegen/box/extensionFunctions/kt1061.kt

@@ -1,7 +1,7 @@
 //KT-1061 Can't call function defined as a val
 
 object X {
-    val doit = { (i: Int) -> i }
+    val doit = { i: Int -> i }
 }
 
 fun box() : String = if (X.doit(3) == 3) "OK" else "fail"

compiler/testData/codegen/box/extensionFunctions/kt1290.kt

@@ -6,7 +6,7 @@ class Foo<T>(val filter: (T) -> Boolean) {
     }
 }
 
-fun foo() = Foo({ (i: Int) -> i < 5 }).bar(2)
+fun foo() = Foo({ i: Int -> i < 5 }).bar(2)
 
 fun box() : String {
     if (!foo()) return "fail"

compiler/testData/codegen/box/extensionFunctions/nested2.kt

@@ -1,6 +1,6 @@
 fun box() : String {
   val y = 12
-  val op = { (x:Int) -> (x + y).toString() }
+  val op = { x:Int -> (x + y).toString() }
 
   val op2 : Int.(Int) -> String = { op(this + it) }