- also add tests

This test touches the internals, if Grouper gets refactored this
test should be removed.

This adds clean up of the shared axes `Grouper` objects as part
of removing an axes.

`_reset_loc_form` is required because the locator/formatters end up
bound to the axis objects of the last axes object (all of the Axes in
the group share the same formatter/locator objects but have different
Axis objects so that all but one of the Axis objects can be made not
visible to not over-draw).  If these are not re-bound to a still visible
axes then changing the limits will change the view limits, but not the
tick locations.

closes matplotlib#5663