chore: deprecate /superset/datasources/

[dpgaspar]

SUMMARY

Continuing the effort on deprecating all /superset/ REST API endpoints
Deprecates /superset/datasources/, found no references on superset-frontend

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]

Codecov Report

Merging #22116 (9e37060) into master (ed1f50e) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #22116      +/-   ##
==========================================
+ Coverage   67.00%   67.13%   +0.12%     
==========================================
  Files        1831     1831              
  Lines       70002    70002              
  Branches     7570     7570              
==========================================
+ Hits        46906    46994      +88     
+ Misses      21138    21043      -95     
- Partials     1958     1965       +7     

Flag	Coverage Δ
hive	52.88% <100.00%> (?)
mysql	78.41% <100.00%> (+<0.01%)	⬆️
postgres	78.47% <100.00%> (+<0.01%)	⬆️
presto	52.78% <100.00%> (+<0.01%)	⬆️
python	81.59% <100.00%> (+0.20%)	⬆️
sqlite	76.94% <100.00%> (+<0.01%)	⬆️
unit	51.26% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/views/core.py	76.11% <100.00%> (+0.01%)	⬆️
superset/utils/core.py	90.85% <0.00%> (+0.10%)	⬆️
superset-frontend/src/SqlLab/actions/sqlLab.js	62.85% <0.00%> (+0.16%)	⬆️
superset/connectors/sqla/models.py	91.21% <0.00%> (+0.17%)	⬆️
superset/db_engine_specs/base.py	89.21% <0.00%> (+0.31%)	⬆️
...nts/controls/DateFilterControl/DateFilterLabel.tsx	62.79% <0.00%> (+4.65%)	⬆️
...board/components/nativeFilters/FilterBar/index.tsx	66.18% <0.00%> (+5.75%)	⬆️
superset/db_engine_specs/hive.py	87.35% <0.00%> (+16.20%)	⬆️
...rd/components/nativeFilters/FilterBar/keyValue.tsx	40.74% <0.00%> (+22.22%)	⬆️
superset/db_engines/hive.py	85.18% <0.00%> (+85.18%)	⬆️

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