Fixed KT-2488 Optimizing imports removes references to enum constants when they are referred via short name in code

idea/testData/editor/optimizeImports/kt2488.kt

@@ -0,0 +1,12 @@
+package test
+
+import test.MyEnum.ONE
+
+fun main(args: Array<String>) {
+    println(ONE)
+}
+
+public enum class MyEnum {
+    ONE
+    TWO
+}

idea/testData/editor/optimizeImports/kt2488_after.kt

@@ -0,0 +1,12 @@
+package test
+
+import test.MyEnum.ONE
+
+fun main(args: Array<String>) {
+    println(ONE)
+}
+
+public enum class MyEnum {
+    ONE
+    TWO
+}