WhenWithOnlyElse: don't remove when subject variable if needed

#KT-30975 Fixed

idea/testData/inspectionsLocal/whenWithOnlyElse/subjectVariable/blockElse/multiReference.kt.after

@@ -0,0 +1,11 @@
+fun test() {
+    <caret>val a = create()
+    use(a, a)
+    foo()
+}
+
+fun create(): String = ""
+
+fun use(s: String, t: String) {}
+
+fun foo() {}