Revert "modem: workaround ofono crash"

We already updated our ofono branch to current master (after 1.28),
and this fix is not longer required, as stated in ticket OS#3064.

Related: OS#3064
This reverts commit f8d12196f0.

Change-Id: I884f6d4f3df4f3b4e2ac05e4dba2ad8704697521

src/osmo_gsm_tester/modem.py

@@ -590,7 +590,6 @@ class Modem(MS):
         req_ifaces = self._required_ifaces()
         if self.is_powered():
             self.dbg('Power cycling')
-            MainLoop.sleep(self, 1.0) # workaround for ofono bug OS#3064
             self.power_off()
         else:
             self.dbg('Powering on')