test: add unused testdata for fix

Author: ernado

test/testdata/fix/in/unused.go

@@ -0,0 +1,8 @@
+//args: -Eunused
+package p
+
+type (
+	unused struct{}
+)
+
+func X() {}

test/testdata/fix/out/unused.go

@@ -0,0 +1,8 @@
+//args: -Eunused
+package p
+
+type (
+	unused struct{}
+)
+
+func X() {}