Bluetooth: Remove unnecessary deadlock check

Previously we didn't have the split to priority rx fiber vs "normal"
rx fiber. This meant that we didn't have full control of code that
would run from this fiber and therefore a deadlock check was useful.
The rx priority fiber (where the deadlock could happen) is very well
defined and controlled so the value of this extra check is now quite
minimal.

Change-Id: I8d09cc39ca6548230a973bc8b8231d999dc1dc67
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>