chore: deprecate old Dashboard endpoints

[dpgaspar]

SUMMARY

Removing server side rendered pages endpoints from Dashboard view. Also deprecating:

• dashboard/api/read
• dashboard/api/delete
• dashboard/export_dashboards_form
• dashboardasync/api/read

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• [ ] Has associated issue:
• [ ] Required feature flags:
• [ ] Changes UI
• [ ] Includes DB Migration (follow approval process in SIP-59)
  • [ ] Migration is atomic, supports rollback & is backwards-compatible
  • [ ] Confirm DB migration upgrade and downgrade tested
  • [ ] Runtime estimates and downtime expectations provided
• [ ] Introduces new feature or API
• [ ] Removes existing feature or API

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 83.27%. Comparing base (2e5f3ed) to head (9c58419). Report is 60 commits behind head on master.

Files	Patch %	Lines
superset/views/dashboard/views.py	86.95%	3 Missing :warning:
superset/views/css_templates.py	0.00%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #28399       +/-   ##
===========================================
+ Coverage   60.49%   83.27%   +22.77%     
===========================================
  Files        1931      521     -1410     
  Lines       76241    37259    -38982     
  Branches     8566        0     -8566     
===========================================
- Hits        46122    31026    -15096     
+ Misses      28015     6233    -21782     
+ Partials     2104        0     -2104     

Flag	Coverage Δ
hive	49.11% <83.33%> (-0.06%)	:arrow_down:
javascript	?
mysql	77.25% <83.33%> (?)
postgres	77.35% <83.33%> (?)
presto	53.69% <83.33%> (-0.11%)	:arrow_down:
python	83.27% <83.33%> (+19.78%)	:arrow_up:
sqlite	76.81% <83.33%> (?)
unit	58.38% <83.33%> (+0.76%)	:arrow_up:

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