Revert "fscrypt: add Speck128/256 support"

This reverts commit c16d27eb.

Resolves conflicts with a later CL, a4842a18 "fscrypt: log the
crypto algorithm implementations".

Also leaves the include/uapi/linux/fs.h constants in place to prevent
future accidental re-use.

Bug: 116008047
Change-Id: I2d64d8d3e384400b7bdfc06a353c3844d4ebb377
Signed-off-by: Alistair Strachan <astrachan@google.com>