Drop FDE status checks from DevicePolicyManagerService

Since FDE (Full Disk Encryption) is no longer supported, there is no
need for DevicePolicyManagerService.getEncryptionStatus() to check for
FDE-specific encryption statuses.

There is more that needs to be cleaned up here, but this gets rid of the
dependency on some obsolete StorageManager methods.

Bug: 208476087
Test: atest DevicePolicyManagerTest
Change-Id: I26c3fafc1b134177324de929d3600fb2dd7f4d1d