Keyguard: let the user drag the challenge down if widgets are disabled

for the system clock widget this does not make much sense but due
that our system default is DashClock it makes a lot sense to
allow it to see more content of DashClock extensions

So remove it.

Change-Id: Idb3a3d3e8d10f2362baf19774de68af92173a0c8
Merge pull request #4 from SlimRoms/kk4.4-caf

Keyguard: let the user drag the challenge down if widgets are disabled