Remove deprecated class in rest_framework_gis package

[lucernae]

Small update, will just merge.

Fix deprecated warnings from rest_framework_gis package

[codecov[bot]]

Codecov Report

Merging #271 into develop_v4 will increase coverage by 1.52%. The diff coverage is 100%.

@@              Coverage Diff               @@
##           develop_v4     #271      +/-   ##
==============================================
+ Coverage       52.25%   53.77%   +1.52%     
==============================================
  Files             130       78      -52     
  Lines            4260     3126    -1134     
  Branches          367      273      -94     
==============================================
- Hits             2226     1681     -545     
+ Misses           1955     1382     -573     
+ Partials           79       63      -16

Impacted Files	Coverage Δ
...project/realtime/serializers/volcano_serializer.py	100% <100%> (ø)	:arrow_up:
...ject/realtime/serializers/earthquake_serializer.py	100% <100%> (ø)	:arrow_up:
django_project/user_map/models/user.py
django_project/core/settings/dev.py
django_project/user_map/auth_backend.py
django_project/user_map/models/user_manager.py
django_project/user_map/admin.py
django_project/core/settings/prod.py
django_project/user_map/utilities/decorators.py
...o_project/user_map/management/commands/mail_osm.py
... and 43 more

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