Remove backend tests on old inference

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

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

@@ -1,5 +1,3 @@
-// !LANGUAGE: +NewInference +FunctionalInterfaceConversion +SamConversionPerArgument +SamConversionForKotlinFunctions
-
 // FILE: lib.kt
 
 fun interface Foo {
@@ -26,4 +24,4 @@ inline fun bar2(): String {
 
 // FILE: main.kt
 
-fun box(): String = bar1() + bar2()
+fun box(): String = bar1() + bar2()