Tweak UI for make profile pattern visible

Removing the summary placeholder from Make profile pattern visible
preference, since this preference has nothing to show in its summary.

Bug: 180573775
Test: visual verified
1) Create a work profile through TestDPC
2) Settings -> Security -> disable Use one lock
3) Setting pattern for Work profile lock
4) Observe Make profile pattern visible and check if it's central
aligned

Change-Id: I66b828aa6f719cdefc6b81efcc3c2c9e54cdcaf1