fix: show onhover menu only in edit mode

[pkdotson]

SUMMARY

This pr fixes issue where trash icon shows in markdown component when not in edit mode.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

after
https://user-images.githubusercontent.com/17326228/136568990-52d48775-03d3-4d91-a73f-eab429402259.mov

TESTING INSTRUCTIONS

Trash icon should not show in markdown when not in edit mode.

ADDITIONAL INFORMATION

• [x ] Has associated issue: Fixes [dashboard][markdown] User can remove markdown component in dashboard view mode #16981
• 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 #17034 (e3cd30f) into master (9e980b6) will decrease coverage by 0.01%.
The diff coverage is 55.76%.

❗ Current head e3cd30f differs from pull request most recent head bf3c30d. Consider uploading reports for the commit bf3c30d to get more accurate results

@@            Coverage Diff             @@
##           master   #17034      +/-   ##
==========================================
- Coverage   76.94%   76.92%   -0.02%     
==========================================
  Files        1030     1031       +1     
  Lines       55088    55153      +65     
  Branches     7480     7500      +20     
==========================================
+ Hits        42385    42428      +43     
- Misses      12452    12473      +21     
- Partials      251      252       +1     

Flag	Coverage Δ
javascript	70.88% <55.76%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
superset-frontend/src/setup/setupErrorMessages.ts	0.00% <0.00%> (ø)
...mponents/nativeFilters/FiltersConfigModal/utils.ts	70.37% <33.33%> (-0.52%)	⬇️
...onfigModal/FiltersConfigForm/FiltersConfigForm.tsx	71.60% <35.71%> (-2.23%)	⬇️
.../src/explore/components/controls/SelectControl.jsx	77.61% <75.00%> (-1.08%)	⬇️
...ts/nativeFilters/FiltersConfigModal/FilterTabs.tsx	85.71% <77.77%> (-0.96%)	⬇️
...e/components/controls/SelectAsyncControl/index.tsx	80.48% <80.00%> (-0.60%)	⬇️
...eFilters/FiltersConfigModal/FiltersConfigModal.tsx	89.34% <88.00%> (+0.77%)	⬆️
...nents/ErrorMessage/DatasetNotFoundErrorMessage.tsx	88.88% <88.88%> (ø)
...c/dashboard/components/gridComponents/Markdown.jsx	83.49% <100.00%> (+0.32%)	⬆️

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[AAfghahi]

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