fix(sqllab): avoid unexpected re-rendering on DatabaseSelector

[justinpark]

SUMMARY

This bug has been accidentally introduced from #17044.

Since DatabaseSelector component has an unnecessary key, DatabaseSelector will be re-mounted rather than update whenever currentDatabase object is updated. This causes the unexpected duplicate database list api request.
This commit removes this key so will skip unnecessary re-rendering and data fetching.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before:

After:

TESTING INSTRUCTIONS

go to Sql Editor and check the network list

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

cc: @betodealmeida

[ktmud]

LGTM

[codecov]

Codecov Report

Merging #21141 (85b5bc2) into master (252ceb7) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 85b5bc2 differs from pull request most recent head 61ea48c. Consider uploading reports for the commit 61ea48c to get more accurate results

@@            Coverage Diff             @@
##           master   #21141      +/-   ##
==========================================
- Coverage   66.32%   66.32%   -0.01%     
==========================================
  Files        1772     1772              
  Lines       67651    67653       +2     
  Branches     7205     7205              
==========================================
+ Hits        44867    44868       +1     
- Misses      20941    20942       +1     
  Partials     1843     1843              

Flag	Coverage Δ
javascript	52.08% <100.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...et-frontend/src/components/TableSelector/index.tsx	76.59% <100.00%> (+0.50%)	⬆️
superset-frontend/src/SqlLab/actions/sqlLab.js	59.83% <0.00%> (-0.28%)	⬇️

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