rx: Remove idleDeadDetection

rx: Remove idleDeadDetection

After change Ie0497d24f1bf4ad7d30ab59061f96c3298f47d17,
testing for idleDeadDetection is equivalent to testing if idleDeadTime
is non-zero. The idleDeadDetection field is thus redundant, so remove
it.

Change-Id: Id11f2829167f4de1505cee286dcc7c56b431a5a6
Reviewed-on: http://gerrit.openafs.org/10782
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Daria Brashear <shadow@your-file-system.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>