FIR2IR: don't add SAM conversion for explicit subtype cases

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

@@ -1,24 +1,24 @@
 fun test1(a: Function0<Unit>) {
   when {
-    a is Runnable -> runStatic(r = a /*as Runnable */ /*-> Runnable? */)
+    a is Runnable -> runStatic(r = a /*as Runnable */)
   }
 }
 
 fun test2(a: Function0<Unit>) {
   when {
-    a is Runnable -> J().run1(r = a /*as Runnable */ /*-> Runnable? */)
+    a is Runnable -> J().run1(r = a /*as Runnable */)
   }
 }
 
 fun test3(a: Function0<Unit>) {
   when {
-    a is Runnable -> J().run2(r1 = a /*as Runnable */ /*-> Runnable? */, r2 = a /*as Runnable */ /*-> Runnable? */)
+    a is Runnable -> J().run2(r1 = a /*as Runnable */, r2 = a /*as Runnable */)
   }
 }
 
 fun test4(a: Function0<Unit>, b: Function0<Unit>) {
   when {
-    a is Runnable -> J().run2(r1 = a /*as Runnable */ /*-> Runnable? */, r2 = b /*-> Runnable? */)
+    a is Runnable -> J().run2(r1 = a /*as Runnable */, r2 = b /*-> Runnable? */)
   }
 }
 
@@ -32,7 +32,7 @@ fun test5x(a: Any) {
   when {
     a is Runnable -> { // BLOCK
       a /*as Runnable */ as Function0<Unit> /*~> Unit */
-      J().run1(r = a /*as Runnable */ /*-> Runnable? */)
+      J().run1(r = a /*as Runnable */)
     }
   }
 }