Remove backend tests on old inference

Also remove any mentions of NewInference, and rename some tests.

compiler/testData/codegen/box/delegatedProperty/kt35707.kt

@@ -1,4 +1,3 @@
-// !LANGUAGE: +NewInference
 // ISSUE: KT-35707
 
 import kotlin.reflect.KProperty
@@ -17,4 +16,4 @@ fun box(): String {
     } else {
         "FAIL"
     }
-}
+}