shared/util: Removes ExtractSnapshotName
shared/util: Removes ExtractSnapshotName

ExtractSnapshotName was dangerous to use as it did not validate the lenth of the slice returned when splitting the supplied volume name by the snapshot delimiter (/).

When used with untrusted inputs it could cause a crash.

Additionally it's functionality overlapped with the safer and more feature rich ContainerGetParentAndSnapshotName, so have removed in place of that.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

atxwebs/lxd,stgraber/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,Skarlso/lxd,hallyn/lxd,mjeanson/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,Skarlso/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd,Skarlso/lxd,stgraber/lxd,mjeanson/lxd,Skarlso/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,mjeanson/lxd,stgraber/lxd