CLN: Drop the buffer_lines parameter in read_csv

[gfyoung]

Deprecated back in 0.19.0

xref #13360.

[codecov]

Codecov Report

Merging #18835 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18835      +/-   ##
==========================================
- Coverage   91.64%   91.62%   -0.02%     
==========================================
  Files         154      154              
  Lines       51408    51408              
==========================================
- Hits        47113    47103      -10     
- Misses       4295     4305      +10

Flag	Coverage Δ
#multiple	89.49% <ø> (-0.01%)	⬇️
#single	40.83% <ø> (-0.12%)	⬇️

Impacted Files	Coverage Δ
pandas/io/parsers.py	95.49% <ø> (ø)	⬆️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.68% <0%> (-0.11%)	⬇️
pandas/core/indexes/datetimes.py	95.62% <0%> (-0.1%)	⬇️

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[jreback]

thanks!