Don't send a start when driving the phase-control fermi-motors.

We don't want to start a chopper before the speed is set if the
following command is issued,
  drive mchp 1.3e6 mchs 4000

site_ansto/instrument/pelican/config/chopper/fermimot.tcl

@@ -483,7 +483,6 @@ namespace eval ::chopper {
     global SCode
     
     hset $hpath/$node/control/set_ref_delay $target
-    hset $hpath/$node/control/start 1
     hsetprop $hpath/$node/control timecheck -1
     set readtime [hgetpropval $hpath read_time]
     hsetprop $hpath lastupdate $readtime