Remove backend tests on old inference

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

compiler/testData/codegen/box/funInterface/funInterfaceInheritance.kt

@@ -1,5 +1,3 @@
-// !LANGUAGE: +NewInference +FunctionalInterfaceConversion +SamConversionPerArgument +SamConversionForKotlinFunctions
-
 fun interface Base {
     fun doStuff(): String
 }
@@ -26,4 +24,4 @@ fun box(): String {
     if (runProxy { 10 } != "10") return "fail2"
 
     return runBase { "OK" }
-}
+}