refactor: Removes the CSS files from the Country Map plugin

[michael-s-molina]

SUMMARY

This PR removes the CSS files from the Country Map plugin using Emotion. It also adjusts the styles to match theme configuration and existing components.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

Check that the plugin is very similar to the previous version. We may have color, font, and opacity differences due to theme adjustments.

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 #19538 (677ce5d) into master (1eef923) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #19538      +/-   ##
==========================================
- Coverage   66.60%   66.59%   -0.01%     
==========================================
  Files        1678     1683       +5     
  Lines       64246    64297      +51     
  Branches     6539     6554      +15     
==========================================
+ Hits        42788    42817      +29     
- Misses      19763    19779      +16     
- Partials     1695     1701       +6     

Flag	Coverage Δ
javascript	51.35% <0.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
.../legacy-plugin-chart-country-map/src/CountryMap.js	0.00% <ø> (ø)
...y-plugin-chart-country-map/src/ReactCountryMap.jsx	0.00% <0.00%> (ø)
...rc/explore/components/ExploreChartHeader/index.jsx	41.07% <0.00%> (-8.93%)	⬇️
.../explore/components/ExploreViewContainer/index.jsx	54.39% <0.00%> (-2.60%)	⬇️
superset-frontend/src/SqlLab/App.jsx	0.00% <0.00%> (ø)
superset-frontend/src/profile/App.tsx	0.00% <0.00%> (ø)
...uperset-frontend/src/components/FaveStar/index.tsx	100.00% <0.00%> (ø)
...plugins/legacy-plugin-chart-treemap/src/Treemap.js	0.00% <0.00%> (ø)
...src/components/FilterableTable/FilterableTable.tsx	71.42% <0.00%> (ø)
...ugins/legacy-plugin-chart-sunburst/src/Sunburst.js	0.00% <0.00%> (ø)
... and 11 more

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[geido]

LGTM!