Copter/Blimp: remove redundant home is set check

[peterbarker]

the subequent call will fail if home is not set

[peterbarker]

Can we hold off on this until we see the larger change to allow setting home before the origin? I agree that the two don't need to be linked but it has been a long standing assumption that the origin would be set first so I think we will trip over issues when we break that assumption.

My reading is that without this patch allowing home to be set before origin would re-introduce the bug you fixed 4 years ago :-)

The new check is the correct one - it's the location object you call the change-frame on which is checked for all-zeroes, and if we allow setting home before setting origin then current_location can be all-zeroes!

I'll do the patch to allow setting home without origin being set and see if I'm correct :-)