Remove upperbound pandas 1.2

[itholic]

Fix several incompatible behavior with pandas in iLocIndexer to remove upperbound pandas 1.2.

[codecov-io]

Codecov Report

Merging #2141 (dcbe6a6) into master (0fd088e) will decrease coverage by 0.90%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2141      +/-   ##
==========================================
- Coverage   95.37%   94.46%   -0.91%     
==========================================
  Files          60       60              
  Lines       13694    13702       +8     
==========================================
- Hits        13060    12944     -116     
- Misses        634      758     +124     

Impacted Files	Coverage Δ
databricks/koalas/indexing.py	92.77% <100.00%> (-0.07%)	:arrow_down:
databricks/koalas/usage_logging/__init__.py	27.27% <0.00%> (-65.29%)	:arrow_down:
databricks/koalas/usage_logging/usage_logger.py	47.82% <0.00%> (-52.18%)	:arrow_down:
databricks/conftest.py	93.75% <0.00%> (-6.25%)	:arrow_down:
databricks/koalas/typedef/typehints.py	89.28% <0.00%> (-6.13%)	:arrow_down:
databricks/koalas/__init__.py	88.15% <0.00%> (-3.95%)	:arrow_down:
databricks/koalas/tests/indexes/test_category.py	98.21% <0.00%> (-1.79%)	:arrow_down:
databricks/koalas/tests/indexes/test_datetime.py	98.27% <0.00%> (-1.73%)	:arrow_down:
databricks/koalas/indexes/datetimes.py	95.91% <0.00%> (-1.37%)	:arrow_down:
databricks/koalas/tests/indexes/test_base.py	99.40% <0.00%> (-0.60%)	:arrow_down:
... and 1 more

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[itholic]

Thanks, @ueshin ! Merging :-)

[HyukjinKwon]

@itholic can you make this change in Apache Spark too?

[ueshin]

I filed a JIRA ticket to track the additional changes. https://issues.apache.org/jira/browse/SPARK-34995