wallet: Do not include server symbols

ui_interface is in libbitcoin_server and can not be included in the
wallet because the wallet does not link with server symbols.

src/ui_interface.h

@@ -20,14 +20,6 @@ class connection;
 }
 } // namespace boost
 
-/** General change type (added, updated, removed). */
-enum ChangeType
-{
-    CT_NEW,
-    CT_UPDATED,
-    CT_DELETED
-};
-
 /** Signals for UI communication. */
 class CClientUIInterface
 {