CLN/PERF: remove gc.collect from the setting_with_copy checks as not needed

[jreback]

This doesn't look might much of a perf gain, but in practice the gc collect can happen at odd times, so this change removes this uncertainty (and is much simpler code)

(pandas) bash-3.2$ asv continuous --bench chained_indexing master gc --config asv_bench/asv.conf.json 
· Creating environments
· Discovering benchmarks
· Running 2 total benchmarks (2 commits * 1 environments * 1 benchmarks)
[  0.00%] · For pandas commit d94146cf <master> (round 1/2):
[  0.00%] ·· Building for conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt...........
[  0.00%] ·· Benchmarking conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[ 25.00%] ··· Running (indexing.ChainIndexing.time_chained_indexing--).
[ 25.00%] · For pandas commit ab6cb31d <gc> (round 1/2):
[ 25.00%] ·· Building for conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt...
[ 25.00%] ·· Benchmarking conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[ 50.00%] ··· Running (indexing.ChainIndexing.time_chained_indexing--).
[ 50.00%] · For pandas commit ab6cb31d <gc> (round 2/2):
[ 50.00%] ·· Benchmarking conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[ 75.00%] ··· indexing.ChainIndexing.time_chained_indexing                                                                                                                                                                                      ok
[ 75.00%] ··· ====== ==========
               mode            
              ------ ----------
               None   72.6±5ms 
               warn   67.2±4ms 
              ====== ==========

[ 75.00%] · For pandas commit d94146cf <master> (round 2/2):
[ 75.00%] ·· Building for conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt...
[ 75.00%] ·· Benchmarking conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[100.00%] ··· indexing.ChainIndexing.time_chained_indexing                                                                                                                                                                                      ok
[100.00%] ··· ====== ==========
               mode            
              ------ ----------
               None   69.4±4ms 
               warn   79.5±4ms 
              ====== ==========


BENCHMARKS NOT SIGNIFICANTLY CHANGED.

[codecov]

Codecov Report

Merging #27031 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #27031      +/-   ##
==========================================
- Coverage   91.99%   91.99%   -0.01%     
==========================================
  Files         180      180              
  Lines       50774    50767       -7     
==========================================
- Hits        46711    46701      -10     
- Misses       4063     4066       +3

Flag	Coverage Δ
#multiple	90.63% <100%> (-0.01%)	⬇️
#single	41.86% <10.52%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	94.18% <100%> (-0.02%)	⬇️
pandas/io/gbq.py	88.88% <0%> (-11.12%)	⬇️
pandas/core/frame.py	96.89% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.94% <0%> (+0.1%)	⬆️

---

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[codecov]

Codecov Report

Merging #27031 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #27031      +/-   ##
==========================================
- Coverage   92.04%   92.03%   -0.02%     
==========================================
  Files         180      180              
  Lines       50714    50707       -7     
==========================================
- Hits        46680    46668      -12     
- Misses       4034     4039       +5

Flag	Coverage Δ
#multiple	90.67% <100%> (-0.01%)	⬇️
#single	41.87% <10.52%> (-0.1%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	94.18% <100%> (-0.02%)	⬇️
pandas/io/gbq.py	88.88% <0%> (-11.12%)	⬇️
pandas/core/frame.py	96.89% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.84% <0%> (-0.11%)	⬇️

---

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Powered by Codecov. Last update d94146c...ab6cb31. Read the comment docs.

[jreback]

@pandas-dev/pandas-core ok with this?