Revert "Support Speck encryption."

This reverts commit 49c27c5c.

Remove the Speck encryption support. It was eventually
decided not to allow Speck in Android P, so this code
is no longer needed and wasn't used outside of testing.

Bug: 112009351
Test: Confirmed AES continues to work with FBE.
Change-Id: Ia5458143be5687fff8d541d8fa2c8ee24a369da4