Disallow extension properties with backing fields

#KT-1682 Fixed

compiler/testData/codegen/box/labels/propertyAccessor.kt

@@ -3,27 +3,9 @@ val Int.getter: Int
         return this@getter
     }
 
-var Int.setter1: Int = 2
-    get() {
-        return this@setter1
-    }
-    set(i: Int) {
-        $setter1 = this@setter1
-    }
-
-var Int.setter2: Int = 2
-    set(i: Int) {
-        $setter2 = this@setter2
-    }
-
 fun box(): String {
     val i = 1
     if (i.getter != 1) return "getter failed"
 
-    i.setter1 = 2
-    if (i.setter1 != 1) return "setter1 failed"
-    i.setter2 = 2
-    if (i.setter2 != 1) return "setter2 failed"
-
     return "OK"
-}
+}

compiler/testData/codegen/box/labels/propertyAccessorFunctionLiteral.kt

@@ -5,19 +5,9 @@ val Int.getter: Int
         }.invoke()
     }
 
-var Int.setter: Int = 1
-    set(i: Int) {
-        $setter = {
-            this@setter
-        }.invoke()
-    }
-
 fun box(): String {
     val i = 1
     if (i.getter != 1) return "getter failed"
 
-    i.setter = 2
-    if (i.setter != 1) return "setter failed"
-
     return "OK"
-}
+}

compiler/testData/codegen/box/labels/propertyAccessorInnerExtensionFun.kt

@@ -7,7 +7,8 @@ val Int.getter: Int
     }
 
 
-var Int.setter: Int = 1
+var Int.setter: Int
+    get() = 1
     set(i: Int) {
         val extFun = { Int.() ->
             this@setter
@@ -24,4 +25,4 @@ fun box(): String {
     if (i.setter != 1) return "setter failed"
 
     return "OK"
-}
+}

compiler/testData/codegen/box/labels/propertyAccessorObject.kt

@@ -4,50 +4,16 @@ trait Base {
 
 val Int.getter: Int
     get() {
-        return object: Base {
+        return object : Base {
             override fun foo(): Int {
                 return this@getter
             }
         }.foo()
     }
 
-var Int.setter1: Int = 2
-    set(i: Int) {
-        $setter1 = object: Base {
-            override fun foo(): Int {
-                this@setter1
-                return 1
-            }
-        }.foo()
-    }
-
-
-var Int.setter2: Int = 2
-    get() {
-        return object: Base {
-            override fun foo(): Int {
-                return this@setter2
-            }
-        }.foo()
-    }
-    set(i: Int) {
-        $setter2 = object: Base {
-            override fun foo(): Int {
-                this@setter2
-                return 1
-            }
-        }.foo()
-    }
-
-
 fun box(): String {
     val i = 1
     if (i.getter != 1) return "getter failed"
 
-    i.setter1 = 2
-    if (i.setter1 != 1) return "setter1 failed"
-    i.setter2 = 2
-    if (i.setter2 != 1) return "setter2 failed"
-
     return "OK"
-}
+}