Revert "Introduce ro.crypto.uses_fs_ioc_add_encryption_key property"

This reverts commit 78f80619.

There is no code that reads this system property, logcat already shows
whether the FS keyring is being used, and all devices launching with
Android 11 and later are guaranteed to use the FS keyring anyway.

Bug: 154327249
Change-Id: Id906efedd89d5bcac5370fb141cdbf7848932d95