Revert SVN r4287: Decimate external strobe

Before the change, when a DAQ region used external strobe signals, timing_ext_div was bypassed. The change always routes these signals through the divider, introducing a delay of 2 clocks.

Revert this change since it causes incompatibilities (e.g. BAM firmware) and the only known user of divided external strobes (BCM firmware DAQ 1) stopped using it in SVN r4322.