Remove obsolete comment about isVisiblePatternEnabled()

The comment in LockPatternUtils#isVisiblePatternEnabled() was only
needed because there were two sources of truth for the default value.
Now that there is only one source of truth, it is not needed.

Bug: 270013005
Change-Id: Ia531f84bcedc957393f93222679efae848a82822
Merged-In: Ia531f84bcedc957393f93222679efae848a82822
(cherry picked from commit f62c4d38)