lib/deploy: Don't include version twice in bootmenu title

lib/deploy: Don't include version twice in bootmenu title

In Silverblue right now, the boot menu title looks like this:

    Fedora 29.20190301.0 (Workstation Edition) 29.20190301.0 (ostree)

This is because RPM-OSTree's `mutate-os-release` feature is enabled,
which injects the OSTree version string directly into `VERSION` and
`PRETTY_NAME`. So appending the version string again is a bit redundant.
Let's just do a simple substring check here before adding the version to
the title.

Closes: #1829
Approved by: cgwalters