fix(sql lab): MultiSelector component render twice

[diegomedina248]

SUMMARY

As explained in #20702, when you select more than one table in SQL Lab and try to clear them all, then the component appears to be rerendering twice (or more).

The issue is that the tables are being removed one by one and, specially if the backend persistence is enabled, then, as the backend responds, the value of the select is updated only by that single table.

This PR ensures all tables are deleted at once, preventing the issue.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before:

Screen.Recording.2022-07-14.at.02.15.18.mov

After:

new.mov

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

Fixes #20702

• 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 #20706 (55a29d8) into master (6b0bb80) will increase coverage by 0.00%.
The diff coverage is 88.88%.

❗ Current head 55a29d8 differs from pull request most recent head 74aece8. Consider uploading reports for the commit 74aece8 to get more accurate results

@@           Coverage Diff           @@
##           master   #20706   +/-   ##
=======================================
  Coverage   66.83%   66.83%           
=======================================
  Files        1750     1750           
  Lines       65894    65898    +4     
  Branches     7017     7017           
=======================================
+ Hits        44041    44045    +4     
  Misses      20067    20067           
  Partials     1786     1786           

Flag	Coverage Δ
javascript	51.94% <88.88%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...d/src/SqlLab/components/SqlEditorLeftBar/index.tsx	49.20% <0.00%> (ø)
superset-frontend/src/SqlLab/actions/sqlLab.js	60.44% <100.00%> (+0.22%)	⬆️
...ntend/src/SqlLab/components/TableElement/index.tsx	72.30% <100.00%> (ø)
superset-frontend/src/SqlLab/reducers/sqlLab.js	33.33% <100.00%> (+0.71%)	⬆️

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[Antonio-RiveroMartnez]

Could tables be null or undefined at some point?

[diegomedina248]

In theory no, but added a check there

[EugeneTorap]

@diegomedina248 Thank you for this hot fix!
@michael-s-molina Can we merge it?