Optimize Imports should remove unused import alias

#KT-17375 Fixed

idea/testData/quickfix/optimizeImports/importAlias.kt

@@ -0,0 +1,10 @@
+// "Optimize imports" "true"
+
+import A as B
+<caret>import A as T
+
+class A
+
+fun foo() {
+    B()
+}

idea/testData/quickfix/optimizeImports/importAlias.kt.after

@@ -0,0 +1,9 @@
+// "Optimize imports" "true"
+
+import A as B
+
+class A
+
+fun foo() {
+    B()
+}