Remove backend tests on old inference

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

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

@@ -1,7 +1,4 @@
-// !LANGUAGE: -NewInference
 // TARGET_BACKEND: JVM
-// NB new inference doesn't really work with old JVM back-end.
-
 // WITH_JDK
 // FILE: samConversionsWithSmartCasts.kt
 
@@ -69,4 +66,4 @@ public class J {
     public void run2(Runnable r1, Runnable r2) {}
 
     public static <T> T id(T x) { return x; }
-}
+}