[lfmerge] Clean after checkout when packaging
[lfmerge] Clean after checkout when packaging

When doing a package build of lfmerge-fdo we'll now do a `git clean`
before building the package.

Change-Id: I30d7cd4243473244f2525f359a23d96e6fdf62d7

sillsdev/ci-builder-scripts,sillsdev/ci-builder-scripts,sillsdev/ci-builder-scripts