Support mock testing for DB (SchemaManager)

Remove "private" default constructor to enable subclasses, mock
testing,, etc.

src/java/org/jivesoftware/database/SchemaManager.java

@@ -70,13 +70,6 @@ public class SchemaManager {
      */
     private static final int DATABASE_VERSION = 22;
 
-    /**
-     * Creates a new Schema manager.
-     */
-    SchemaManager() {
-
-    }
-
     /**
      * Checks the Openfire database schema to ensure that it's installed and up to date.
      * If the schema isn't present or up to date, an automatic update will be attempted.