remove backwards-compatibility alias `Adaptor`

[Sergey Fedoseev]

All spatial operations classes have Adaptor class attribute and comments say that it backwards-compatibility alias for Adapter. This attribute was added to fix #13315.

It seems however that it doesn't provide any backwards-compatibility. Quoting comment from mentioned ticket:

It's a matter of debate to whether this is a backwards-incompatible change -- the root cause of the issue is that SpatialBackend (and SpatialBackend.Adaptor) no longer exists due to multiple-database support, however, it was never documented to begin with.

I did indeed rename the Adaptor objects to the more common spelling of Adapter; providing aliases is a possibility -- however, I also changed the root namespace to django.contrib.gis.db.backends (the s was added), thus even the aliases wouldn't even be truly backwards-compatible.

As could be seen from comments of that ticket it was proposed to add this alias to deprecation timeline, but for some reason this wasn't done.

[Sergey Fedoseev]

PR -- ​https://github.com/django/django/pull/5746

[Tim Graham <timograham@…>]

In 49f1cc5:

Fixed #25835 -- Removed Adaptor alias from spatial operations classes.