Revert^2 "MGF1 Digest setter: Handle case of flag off"

This reverts commit 468c8fe6.
Additionally, this adds a guard for reading the flag: If
the calling app does not have the right permission to read the device
configuration, the code will assume it is not set.

Reason for revert: Fixed flag reading code

Bug: 314744703
Test: atest CtsWebkitTestCases:android.webkit.cts.WebViewSslTest#testProceedClientCertRequestKeyWithAndroidKeystoreKey
Change-Id: I29c58bc8c5960c0ab9af70f93440bd9a1db12dc7