Remove amqp from the BACKEND_ALISES list

[Kludex]

• Fixes No module named 'celery.backends.amqp' or KeyError: 'backend' #6384

[codecov]

Codecov Report

Base: 89.59% // Head: 89.59% // No change to project coverage 👍

Coverage data is based on head (8b494be) compared to base (64f7e89).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7805   +/-   ##
=======================================
  Coverage   89.59%   89.59%           
=======================================
  Files         128      128           
  Lines       15877    15877           
  Branches     2117     2117           
=======================================
  Hits        14225    14225           
  Misses       1423     1423           
  Partials      229      229           

Flag	Coverage Δ
unittests	89.57% <ø> (ø)

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Impacted Files	Coverage Δ
celery/app/backends.py	100.00% <ø> (ø)

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[Kludex]

Thanks @auvipy 🙏