update function name

UpdateUsesCompression ended up becoming a historical misnomer when we
transititioned from dm-snapshot to userspace snapshots. Initially this
transitiion is what allowed us to add compression to the snapshots,
however userspace snapshot also supports an uncompressed format, leading
to a confusing function name. Since dm-snapshot is no longer supported
let's rename this function

Test: th
Change-Id: I72909d9200abaa78bfbf86ae1a2e6555cbf0e308