Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/extensionFunctions/nested2.kt

@@ -1,8 +0,0 @@
-fun box() : String {
-  val y = 12
-  val op = { (x:Int) -> (x + y).toString() }
-
-  val op2 : Int.(Int) -> String = { op(this + it) }
-
-  return if("27" == 5.op2(10)) "OK" else "fail"
-}

compiler/testData/codegen/extensionFunctions/shared.kt

@@ -1,13 +0,0 @@
-fun <T> T.mustBe(t : T) {
-    assert("$this must be $t") {this == t}
-}
-
-inline fun assert(message : String, condition : () -> Boolean) {
-    if (!condition())
-        throw AssertionError(message)
-}
-
-fun box() : String {
-    "lala" mustBe "lala"
-    return "OK"
-}

compiler/testData/codegen/extensionFunctions/virtual.kt

@@ -1,24 +0,0 @@
-class Request(val path: String) {
-
-}
-
-class Handler() {
-    fun Int.times(op: ()-> Unit) {
-        for(i in 0..this)
-            op()
-    }
-
-//    fun Request.getPath() : String {
-//        val sb = java.lang.StringBuilder()
-//        10.times {
-//            sb.append(path)?.append(this)
-//        }
-//        return sb.toString() as String
-//    }
-
-    fun Request.getPath() = path
-
-    fun test(request: Request) = request.getPath()
-}
-
-fun box() : String = if(Handler().test(Request("239")) == "239") "OK" else "fail"