Change String param to CharSequence

Change String param in DisableSecureLockDeviceParams and
EnableSecureLockDeviceParams to CharSequence to match API guidelines

Flag: android.security.secure_lockdown
Fixes: 379894299
API-Coverage-Bug: 376456619
Test: N/A
Ignore-AOSP-First: under flag in security package
Change-Id: I284652b9dfc5161c77a7597055e19f03c7bd3e0e