Remove backend tests on old inference

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

compiler/testData/ir/irText/expressions/sam/samConversionsWithSmartCasts.kt.txt

@@ -25,7 +25,7 @@ fun test3(a: Function0<Unit>) {
 fun test4(a: Function0<Unit>, b: Function0<Unit>) {
   when {
     a is Runnable -> { // BLOCK
-      J().run2(r1 = a /*-> @FlexibleNullability Runnable? */, r2 = b /*-> @FlexibleNullability Runnable? */)
+      J().run2(r1 = a /*as Runnable */, r2 = b /*-> @FlexibleNullability Runnable? */)
     }
   }
 }