Revert "Rename Extension annotation to ExtensionFunctionType"

This reverts commit 460dad135c.

The old compiler will not see the new runtime correctly. Postponing this until
1.0

compiler/testData/resolvedCalls/invoke/implicitReceiverForInvoke.txt

@@ -11,5 +11,5 @@ Resolved call:
 Resulting descriptor: operator fun Int.invoke(): Unit defined in kotlin.Function1
 
 Explicit receiver kind = DISPATCH_RECEIVER
-Dispatch receiver = f {[@kotlin.ExtensionFunctionType] Function1<Int, Unit>}
+Dispatch receiver = f {[@kotlin.Extension] Function1<Int, Unit>}
 Extension receiver = IntExt{fun Int.<anonymous>(): Unit defined in bar}