Remove constrained_layout from arviz rcparams

[aloctavodia]

Fixes #1763 and this is also related to #1247

[codecov]

Codecov Report

Merging #1764 (45c75dc) into main (956a8cc) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1764      +/-   ##
==========================================
- Coverage   91.23%   91.23%   -0.01%     
==========================================
  Files         117      117              
  Lines       12443    12441       -2     
==========================================
- Hits        11352    11350       -2     
  Misses       1091     1091              

Impacted Files	Coverage Δ
arviz/plots/backends/matplotlib/__init__.py	96.36% <ø> (-0.07%)	⬇️
arviz/plots/backends/matplotlib/pairplot.py	92.10% <ø> (-0.05%)	⬇️
arviz/rcparams.py	94.16% <ø> (ø)
arviz/plots/backends/matplotlib/khatplot.py	73.07% <100.00%> (ø)

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