pgsql-server: Remove duplicate PQclear(res) operations leading to double

Log Message:
-----------
Remove duplicate PQclear(res) operations leading to double free() and
subsequent core dump. It looks like at one time DBLINK_RES_ERROR_AS_NOTICE
didn't include a PQclear, but now it does and so these other ones are
duplicate.

Modified Files:
--------------
pgsql-server/contrib/dblink:
dblink.c (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/contrib/dblink/dblink.c.diff?r1=1.34&r2=1.35)