Remember to drop roles created by regression tests.

Commit e3920ac8 created "regress_subscription_user2" in subscription.sql,
but forgot to drop it, causing the regression tests to fail if run twice
without re-initdb'ing.

src/test/regress/expected/subscription.out

@@ -119,4 +119,5 @@ DROP SUBSCRIPTION testsub NODROP SLOT;  -- fail
 ERROR:  subscription "testsub" does not exist
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_subscription_user;
+DROP ROLE regress_subscription_user2;
 DROP ROLE regress_subscription_user_dummy;

src/test/regress/sql/subscription.sql

@@ -92,4 +92,5 @@ DROP SUBSCRIPTION testsub NODROP SLOT;  -- fail
 
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_subscription_user;
+DROP ROLE regress_subscription_user2;
 DROP ROLE regress_subscription_user_dummy;