Remove unused support for partial encryption

Commit 87999173dd79 ("Don't corrupt ssd when encrypting and power
fails") added a lot of code to handle pausing in-place conversion from
unencrypted => FDE when the battery was low, and resuming it later.

It was eventually decided that this wasn't needed, and commit
7e17e2d22678 ("Don't worry about battery levels when encrypting")
removed the checks for low battery.

This made the partial encryption code unused.  So remove it.

Note that this was cluttering up the metadata encryption code too, since
EncryptInplace.cpp is now shared by both FDE and metadata encryption.

Bug: 16868177
Test: see I08fc8465f7962abd698904b5466f3ed080d53953
Change-Id: Ibd2eb08a2aa15938097abcb8a67b5a813c4d76c7
4 files changed