[FIR2IR] Don't insert not-needed upcasts for smartcasted expressions

Related to KT-63257

compiler/testData/ir/irText/expressions/suspendConversionOnArbitraryExpression.fir.kt.txt

@@ -175,13 +175,13 @@ fun testSmartCastOnVarWithSuspendConversion(a: Any) {
 
 fun testSmartCastVsSuspendConversion(a: Function0<Unit>) {
   a as SuspendFunction0<Unit> /*~> Unit */
-  useSuspend(sfn = a /*as Function<Unit> */)
+  useSuspend(sfn = a)
 }
 
 fun testSmartCastOnVarVsSuspendConversion(a: Function0<Unit>) {
   var b: Function0<Unit> = a
   b as SuspendFunction0<Unit> /*~> Unit */
-  useSuspend(sfn = b /*as Function<Unit> */)
+  useSuspend(sfn = b)
 }
 
 fun <T> testIntersectionVsSuspendConversion(x: T) where T : Function0<Unit>, T : SuspendFunction0<Unit> {