lxd: remove remaining DiskIdmap call in startCommon()
lxd: remove remaining DiskIdmap call in startCommon()

The idmapType will only be != idmap.IdmapStorageNone if diskIdmap is
nil so that check adds more confusion as it implies it can be that
idmapType != idmap.IdmapStorageNone while diskIdmap is non-nil.

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@ubuntu.com>

stgraber/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd