Turning off dockets for `all_world2pix()`

I do not think it is possible to get doctests to pass with the examples
in `all_world2pix`, at least I do not know how. In addition, I do not
think this is essential: documentation builds alright, and unit tests
are OK... So, investing time in trying to fix doctests will not bring
any benefits.

The problem with doctests, I think, is that in my examples there are
print statements inside except blocks and doctests have problems when
except blocks produce anything additional to the regular traceback.