fix: Alembic migration 18532d70ab98

[john-bodley]

SUMMARY

This PR reverts some of the logic from this commit as it seems that this constraint may not exist for all MySQL deployments resulting in the migration to fail.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

Ran

superset db upgrade
superset db downgrade

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov-commenter]

Codecov Report

Merging #11136 into master will decrease coverage by 4.18%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #11136      +/-   ##
==========================================
- Coverage   65.84%   61.66%   -4.19%     
==========================================
  Files         826      826              
  Lines       39016    39016              
  Branches     3667     3667              
==========================================
- Hits        25689    24058    -1631     
- Misses      13217    14777    +1560     
- Partials      110      181      +71     

Flag	Coverage Δ
#cypress	?
#javascript	62.21% <ø> (ø)
#python	61.33% <0.00%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
...532d70ab98_fix_table_unique_constraint_in_mysql.py	0.00% <0.00%> (ø)
superset-frontend/src/SqlLab/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/index.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/index.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupColors.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/chart/ChartContainer.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupFormatters.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/reducers/index.js	0.00% <0.00%> (-100.00%)	⬇️
... and 169 more

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[dpgaspar]

Thank you @john-bodley