CLN: remove Panel-specific parts of core.generic

[simonjayhawkins]

xref #25632

removed small amount of code related to self.ndim > 2

also a few changes to make the NotImplemented errors for self.ndim>2 more consistent and added test for these. (might be worth having a decorator for these)

[codecov]

Codecov Report

Merging #26738 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26738      +/-   ##
==========================================
+ Coverage   91.78%   91.79%   +<.01%     
==========================================
  Files         174      174              
  Lines       50703    50695       -8     
==========================================
- Hits        46538    46533       -5     
+ Misses       4165     4162       -3

Flag	Coverage Δ
#multiple	90.38% <100%> (+0.01%)	⬆️
#single	41.81% <0%> (-0.08%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	93.94% <100%> (+0.3%)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

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[codecov]

Codecov Report

Merging #26738 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26738      +/-   ##
==========================================
+ Coverage   91.78%   91.78%   +<.01%     
==========================================
  Files         174      174              
  Lines       50703    50683      -20     
==========================================
- Hits        46538    46521      -17     
+ Misses       4165     4162       -3

Flag	Coverage Δ
#multiple	90.38% <100%> (+0.01%)	⬆️
#single	41.82% <0%> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	93.91% <100%> (+0.27%)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3937fbc...a2cedd7. Read the comment docs.

[jreback]

actually I wouldn't worry about checking ndim at all in any methods and just remove all of the checks.

[simonjayhawkins]

sounds good. thanks.

[topper-123]

Thanks, @simonjayhawkins!