refactor: Removes the CSS files from the Paired T-Test plugin

[michael-s-molina]

SUMMARY

This PR removes the CSS files from the Paired T-Test 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 #19563 (216c56c) into master (2de5e6f) will decrease coverage by 0.00%.
The diff coverage is 31.03%.

❗ Current head 216c56c differs from pull request most recent head a441291. Consider uploading reports for the commit a441291 to get more accurate results

@@            Coverage Diff             @@
##           master   #19563      +/-   ##
==========================================
- Coverage   66.66%   66.65%   -0.01%     
==========================================
  Files        1678     1680       +2     
  Lines       64261    64273      +12     
  Branches     6561     6564       +3     
==========================================
+ Hits        42837    42842       +5     
- Misses      19723    19729       +6     
- Partials     1701     1702       +1     

Flag	Coverage Δ
javascript	51.46% <31.03%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...et-ui-chart-controls/src/shared-controls/index.tsx	36.19% <ø> (ø)
.../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)
...acy-plugin-chart-paired-t-test/src/PairedTTest.jsx	0.00% <0.00%> (ø)
...y-plugin-chart-sankey-loop/src/ReactSankeyLoop.jsx	0.00% <0.00%> (ø)
.../legacy-plugin-chart-sankey-loop/src/SankeyLoop.js	0.00% <ø> (ø)
...lugin-chart-echarts/src/BigNumber/BigNumberViz.tsx	0.00% <0.00%> (ø)
...src/BigNumber/BigNumberWithTrendline/buildQuery.ts	0.00% <0.00%> (-11.12%)	⬇️
.../BigNumber/BigNumberWithTrendline/controlPanel.tsx	33.33% <ø> (ø)
superset-frontend/src/SqlLab/actions/sqlLab.js	60.39% <0.00%> (-0.35%)	⬇️
... and 5 more

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