Remove underlines from focused links

[Nouzbe]

This is a ...

• Component style update

What's the background?

This PR removes underlines from focused links.
It avoids an appearing/disappearing underline when hovering a focused link.
See #15725.

API Realization

The API is unchanged.

What's the affect?

Focused links are not underlined.

Self Check before Merge

• Doc not needed
• Demo not needed
• TypeScript definition not needed
• Changelog provided (just above)

Additional Plan?

No.

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[codecov]

Codecov Report

Merging #15759 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #15759      +/-   ##
==========================================
+ Coverage   94.96%   95.03%   +0.06%     
==========================================
  Files         250      250              
  Lines        6640     6640              
  Branches     1907     1907              
==========================================
+ Hits         6306     6310       +4     
+ Misses        333      329       -4     
  Partials        1        1

Impacted Files	Coverage Δ
components/form/FormItem.tsx	98.85% <0%> (+2.28%)	⬆️

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[codecov]

Codecov Report

Merging #15759 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #15759      +/-   ##
==========================================
+ Coverage   94.96%   95.03%   +0.06%     
==========================================
  Files         250      250              
  Lines        6640     6640              
  Branches     1907     1907              
==========================================
+ Hits         6306     6310       +4     
+ Misses        333      329       -4     
  Partials        1        1

Impacted Files	Coverage Δ
components/form/FormItem.tsx	98.85% <0%> (+2.28%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b56d651...765dcc3. Read the comment docs.