Remove unused setup_tables

Setup tables was called twice.

Change-Id: Idd937e1844689edfadbfeb2e180a8ab497c29ec9
diff --git a/zuul/driver/sql/sqlconnection.py b/zuul/driver/sql/sqlconnection.py
index b964c0b..41f0933 100644
--- a/zuul/driver/sql/sqlconnection.py
+++ b/zuul/driver/sql/sqlconnection.py
@@ -49,7 +49,6 @@
                 poolclass=sqlalchemy.pool.QueuePool,
                 pool_recycle=self.connection_config.get('pool_recycle', 1))
             self._migrate()
-            self._setup_tables()
             self.zuul_buildset_table, self.zuul_build_table \
                 = self._setup_tables()
             self.tables_established = True