feat: stop setting MeetingRegistration.attended on MeetEcho login.

[rjsparks]

We capture attendence through MeetEcho using meeting.Attended now.

[rjsparks]

cc @rpcross @alexamirante

[codecov]

Codecov Report

Merging #4526 (ff9bde8) into main (d3f25a6) will decrease coverage by 0.00%.
The diff coverage is 85.36%.

@@            Coverage Diff             @@
##             main    #4526      +/-   ##
==========================================
- Coverage   88.43%   88.42%   -0.01%     
==========================================
  Files         296      296              
  Lines       39674    39679       +5     
==========================================
+ Hits        35086    35088       +2     
- Misses       4588     4591       +3     

Impacted Files	Coverage Δ
ietf/ietfauth/utils.py	92.76% <ø> (+2.02%)	⬆️
ietf/doc/utils.py	88.12% <66.66%> (-0.46%)	⬇️
ietf/api/views.py	89.06% <100.00%> (+0.17%)	⬆️
ietf/doc/views_doc.py	90.88% <100.00%> (+0.34%)	⬆️
ietf/doc/views_search.py	89.23% <100.00%> (ø)
ietf/group/forms.py	91.41% <100.00%> (+0.16%)	⬆️
ietf/nomcom/utils.py	91.28% <100.00%> (-0.17%)	⬇️
ietf/nomcom/views.py	96.73% <100.00%> (+<0.01%)	⬆️
ietf/stats/utils.py	53.81% <100.00%> (ø)
ietf/submit/utils.py	93.60% <100.00%> (-0.02%)	⬇️
... and 6 more

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