Do not run unused symbol inspection on default objects for now

#KT-6872 Fixed

idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt

@@ -126,6 +126,8 @@ public class UnusedSymbolInspection : AbstractKotlinInspection() {
                 if (declaration is JetProperty && declaration.isLocal()) return
                 if (declaration is JetParameter && (declaration.getParent()?.getParent() !is JetClass || !declaration.hasValOrVarNode())) return
                 if (declaration is JetNamedFunction && isConventionalName(declaration)) return
+                //TODO: support this inspection for class objects
+                if (declaration is JetObjectDeclaration && declaration.isClassObject()) return
 
                 // More expensive, resolve-based checks
                 if (isEntryPoint(declaration)) return

idea/testData/inspections/unusedSymbol/object/defaultObject.kt

@@ -0,0 +1,23 @@
+package defaultObject
+
+class A {
+    class object {
+    }
+}
+
+class B {
+    class object NamedUnused {
+    }
+}
+
+class C {
+    class object NamedUsed {
+    }
+}
+
+fun main(args: Array<String>) {
+    A()
+    B()
+    C()
+    C.NamedUsed
+}