CLN: remove unused mgr kwarg

[jbrockmendel]

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

[pep8speaks]

Hello @jbrockmendel! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/internals/blocks.py !

• There are no PEP8 issues in the file pandas/core/internals/managers.py !

[jbrockmendel]

This is the only place where the passed mgr is ever used. I think we can get axes out too, but am holding off on that.

[jreback]

looks fine, ping on green.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@779aeac). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master   #23260   +/-   ##
=========================================
  Coverage          ?   92.22%           
=========================================
  Files             ?      169           
  Lines             ?    50904           
  Branches          ?        0           
=========================================
  Hits              ?    46947           
  Misses            ?     3957           
  Partials          ?        0

Flag	Coverage Δ
#multiple	90.65% <100%> (?)
#single	42.29% <85.71%> (?)

Impacted Files	Coverage Δ
pandas/core/internals/managers.py	95.73% <100%> (ø)
pandas/core/internals/blocks.py	94.08% <100%> (ø)

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[TomAugspurger]

All green.