FIR checker: warn useless elvis

compiler/testData/diagnostics/tests/callableReference/generic/specialCalls.fir.kt

@@ -1,23 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER, -UNUSED_VARIABLE
-
-fun baz(i: Int) = i
-fun <T> bar(x: T): T = TODO()
-
-fun nullableFun(): ((Int) -> Int)? = null
-
-fun test() {
-    val x1: (Int) -> Int = bar(if (true) ::baz else ::baz)
-    val x2: (Int) -> Int = bar(nullableFun() ?: ::baz)
-    val x3: (Int) -> Int = bar(::baz ?: ::baz)
-
-    val i = 0
-    val x4: (Int) -> Int = bar(when (i) {
-                                   10 -> ::baz
-                                   20 -> ::baz
-                                   else -> ::baz
-                               })
-
-    val x5: (Int) -> Int = bar(::baz<!NOT_NULL_ASSERTION_ON_CALLABLE_REFERENCE!>!!<!>)
-
-    (if (true) ::baz else ::baz)(1)
-}

compiler/testData/diagnostics/tests/callableReference/generic/specialCalls.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER, -UNUSED_VARIABLE
 
 fun baz(i: Int) = i

compiler/testData/diagnostics/tests/callableReference/withQuestionMarks.fir.kt

@@ -24,8 +24,8 @@ fun main() {
     val x17 = <!UNRESOLVED_REFERENCE!>logger<!>::info<!NOT_NULL_ASSERTION_ON_CALLABLE_REFERENCE!>!!<!>?::<!UNRESOLVED_REFERENCE!>print<!>?::<!UNRESOLVED_REFERENCE!>print<!>
 
     // It must be OK
-    val x18 = String?::hashCode ?: ::foo
-    val x19 = String::hashCode ?: ::foo
+    val x18 = String?::hashCode <!USELESS_ELVIS!>?: ::foo<!>
+    val x19 = String::hashCode <!USELESS_ELVIS!>?: ::foo<!>
     val x20 = String?::hashCode::hashCode
     val x21 = kotlin.String?::hashCode::hashCode
 }