purge: milestones + updates

[thelostone-mc]

Description

• remove milestones and updates from grants
• this has already been removed from UI

[codecov]

Codecov Report

Merging #6370 into master will decrease coverage by 0.09%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master    #6370      +/-   ##
==========================================
- Coverage   27.54%   27.45%   -0.10%     
==========================================
  Files         286      286              
  Lines       26211    26144      -67     
  Branches     3867     3861       -6     
==========================================
- Hits         7219     7177      -42     
+ Misses      18727    18698      -29     
- Partials      265      269       +4     

Impacted Files	Coverage Δ
app/dashboard/models.py	49.69% <ø> (ø)
app/grants/forms.py	0.00% <0.00%> (-100.00%)	⬇️
app/grants/models.py	48.38% <ø> (-1.16%)	⬇️
app/grants/urls.py	100.00% <ø> (ø)
app/inbox/models.py	93.33% <ø> (ø)
app/grants/views.py	15.48% <50.00%> (+0.47%)	⬆️
app/grants/admin.py	42.46% <100.00%> (-2.99%)	⬇️
app/grants/serializers.py	100.00% <100.00%> (ø)
app/dashboard/views.py	11.15% <0.00%> (ø)
... and 2 more

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