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/builtin-classes.txt

@@ -464,14 +464,10 @@ public abstract class Enum</*0*/ E : kotlin.Enum<E>> : kotlin.Comparable<E> {
     }
 }
 
-@kotlin.annotation.Target(allowedTargets = {AnnotationTarget.TYPE}) @kotlin.annotation.MustBeDocumented() @kotlin.Deprecated(message = "Use @ExtensionFunctionType instead.", replaceWith = kotlin.ReplaceWith(expression = "@ExtensionFunctionType", imports = {})) public final annotation class Extension : kotlin.Annotation {
+@kotlin.annotation.Target(allowedTargets = {AnnotationTarget.TYPE}) @kotlin.annotation.MustBeDocumented() public final annotation class Extension : kotlin.Annotation {
     /*primary*/ public constructor Extension()
 }
 
-@kotlin.annotation.Target(allowedTargets = {AnnotationTarget.TYPE}) @kotlin.annotation.MustBeDocumented() public final annotation class ExtensionFunctionType : kotlin.Annotation {
-    /*primary*/ public constructor ExtensionFunctionType()
-}
-
 public final class Float : kotlin.Number, kotlin.Comparable<kotlin.Float> {
     /*primary*/ private constructor Float()
     public final operator fun compareTo(/*0*/ other: kotlin.Byte): kotlin.Int