drop gdisk from install packages in debian
debian/install.py has the following:
- ceph only recommends gdisk, make sure we actually have
- it; only really needed for osds, but minimal collateral
And the installs gdisk unconditionally. However, looking at debian/control, the "ceph" package has required gdisk (not recommended) at least since firefly:
It can be safely removed from the code, and we can allow it be pulled in by dependency.