chore: Remove unused sliceCanEdit logic

[john-bodley]

SUMMARY

#24266 is failing as—for some unknown reason—the can_slice permission is missing. It turns out—thanks to help from @michael-s-molina—that the permission is unused (outside of testing). This PR removes the unused logic which in turn should hopefully unblock #24266.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

CI.

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 #24312 (4d27e28) into master (9c7b8b8) will decrease coverage by 0.09%.
The diff coverage is n/a.

❗ Current head 4d27e28 differs from pull request most recent head cfb09ea. Consider uploading reports for the commit cfb09ea to get more accurate results

@@            Coverage Diff             @@
##           master   #24312      +/-   ##
==========================================
- Coverage   68.33%   68.24%   -0.09%     
==========================================
  Files        1957     1957              
  Lines       75627    75626       -1     
  Branches     8225     8224       -1     
==========================================
- Hits        51679    51613      -66     
- Misses      21835    21900      +65     
  Partials     2113     2113              

Flag	Coverage Δ
hive	?
javascript	54.76% <ø> (-0.01%)	⬇️
mysql	78.92% <ø> (ø)
postgres	79.00% <ø> (ø)
presto	53.32% <ø> (ø)
python	82.64% <ø> (-0.18%)	⬇️
sqlite	77.53% <ø> (ø)
unit	53.44% <ø> (ø)

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

Impacted Files	Coverage Δ
superset-frontend/src/dashboard/actions/hydrate.js	2.04% <ø> (ø)
...end/src/dashboard/components/SliceHeader/index.tsx	90.56% <ø> (-0.18%)	⬇️
...dashboard/components/SliceHeaderControls/index.tsx	69.79% <ø> (ø)
.../src/dashboard/components/gridComponents/Chart.jsx	57.52% <ø> (ø)
...perset-frontend/src/dashboard/containers/Chart.jsx	75.00% <ø> (ø)

... and 4 files with indirect coverage changes

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[michael-s-molina]

LGTM