remove needless error checking on disconnect

lib/dialects/mssql/connection-manager.js

@@ -93,11 +93,6 @@ ConnectionManager.prototype.disconnect = function(connection) {
   }
 
   return new Promise(function (resolve, reject) {
-    connection.on('error', function(err) {
-      // TODO: error checking
-      reject();
-    });
-
     connection.on('end', resolve);
     connection.close();
   });