rx: Remove warning inhibition on rx.c

The CFLAGS_NOERROR rule for rx.c seems to have crept back in as
part of the libtool changes. The LWP build of rx.c has never had
warning inhibition on rx.c, and the inhibition in the pthread
builds was removed by 327762071be3806c5d08be0218982c7027754756

Change-Id: Icde3f0b6ee2f8ae0818a3dc722c6171284d6a9e6
Reviewed-on: http://gerrit.openafs.org/8921
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>