postgresql: Fix redundant rpath for '/usr/lib'

This patch fixes the following QA issue:

,----[ Fragment of build error log ]
| ...
| ERROR: QA Issue: postgresql-client:
|   /work/.../usr/bin/pg_dumpall contains probably-redundant
|   RPATH /usr/lib
| ...
`----

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Reported-by: Nathan West <nate.ewest@gmail.com>
Reported-by: Rogerio Pimentel <rogerio.pimentel@freescale.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>