Don't allow LOCK_PATTERN_* settings to be read with no permission

Eliminate the exception for the three LOCK_PATTERN_* settings in
LockSettingsService.checkDatabaseReadPermission().

To do this, make the public API android.provider.Settings.Secure stop
calling ILockSettings.getString() for these settings for apps targeting
a pre-M API level.  Instead, just always return "0".

This should be very safe, since not only have pre-M target API levels
mostly been phased out, but the only one of these settings that didn't
*already* always return "0" was LOCK_PATTERN_VISIBLE.  That one was
unlikely to be used by apps, as it just indicated whether the user had
the "Make pattern visible" preference enabled the last time they had a
pattern; it didn't reliably indicate whether the user actually had a
pattern.  Only LOCK_PATTERN_ENABLED is known to have been used by an
app, and that has returned "0" since Android 11 due to commit
a486e2d7 (http://ag/10400376) moving the special-case handling of
LOCK_PATTERN_ENABLED into getBoolean() instead of getString().

Finally, remove the special-case handling of LOCK_PATTERN_ENABLED from
getBoolean(), as it's clearly not needed.  This change removes the only
potential user, but the code was in the wrong place for it anyway.

Bug: 204903437
Merged-In: If7a47ae9c3834e6a9a14900e86bc5a68c7cbdc97
Change-Id: If7a47ae9c3834e6a9a14900e86bc5a68c7cbdc97