Remove extraneous brackets

[deepyaman]

Trivial documentation changes

Dictionary should have one set of brackets (as seen below in documentation example {'a': np.float64, 'b': np.int32}).

Brackets don't make sense around 'w' or 'a'.

• closes #xxxx
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #26375 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26375      +/-   ##
==========================================
- Coverage   91.68%   91.67%   -0.01%     
==========================================
  Files         174      174              
  Lines       50703    50703              
==========================================
- Hits        46488    46484       -4     
- Misses       4215     4219       +4

Flag	Coverage Δ
#multiple	90.18% <ø> (ø)	⬆️
#single	41.19% <ø> (-0.15%)	⬇️

Impacted Files	Coverage Δ
pandas/io/excel/_base.py	92.13% <ø> (ø)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	97.01% <0%> (-0.12%)	⬇️

---

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[codecov]

Codecov Report

Merging #26375 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26375      +/-   ##
==========================================
- Coverage   91.68%   91.67%   -0.01%     
==========================================
  Files         174      174              
  Lines       50703    50704       +1     
==========================================
- Hits        46488    46485       -3     
- Misses       4215     4219       +4

Flag	Coverage Δ
#multiple	90.18% <ø> (ø)	⬆️
#single	41.19% <ø> (-0.15%)	⬇️

Impacted Files	Coverage Δ
pandas/io/excel/_base.py	92.13% <ø> (ø)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	97.01% <0%> (-0.12%)	⬇️
pandas/core/indexes/base.py	96.72% <0%> (ø)	⬆️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[WillAyd]

Thanks!