fix dropping table without autoincrement trigger in Oracle

lib/Doctrine/DBAL/Schema/OracleSchemaManager.php

@@ -311,7 +311,7 @@ class OracleSchemaManager extends AbstractSchemaManager
      */
     public function dropTable($name)
     {
-        $this->dropAutoincrement($name);
+        $this->tryMethod('dropAutoincrement', $name);
 
         parent::dropTable($name);
     }