Fix sloppy cleanup of roles in privileges.sql.

Commit 3d14e17 dropped regress_roleoption_donor twice and
regress_roleoption_protagonist not at all.  Leaving roles behind
after "make installcheck" is unfriendly in its own right, plus
it causes repeated runs of "make installcheck" to fail.

Author: tglsfdc

src/test/regress/expected/privileges.out

@@ -2846,7 +2846,6 @@ DROP TABLE regress_roleoption.t2;
 DROP TABLE regress_roleoption.t3;
 DROP TABLE regress_roleoption.t4;
 DROP SCHEMA regress_roleoption;
-DROP ROLE regress_roleoption_recipient;
-DROP ROLE regress_roleoption_donor;
+DROP ROLE regress_roleoption_protagonist;
 DROP ROLE regress_roleoption_donor;
-ERROR:  role "regress_roleoption_donor" does not exist
+DROP ROLE regress_roleoption_recipient;

src/test/regress/sql/privileges.sql

@@ -1849,6 +1849,6 @@ DROP TABLE regress_roleoption.t2;
 DROP TABLE regress_roleoption.t3;
 DROP TABLE regress_roleoption.t4;
 DROP SCHEMA regress_roleoption;
-DROP ROLE regress_roleoption_recipient;
-DROP ROLE regress_roleoption_donor;
+DROP ROLE regress_roleoption_protagonist;
 DROP ROLE regress_roleoption_donor;
+DROP ROLE regress_roleoption_recipient;