Fix identical and equals for the comparison between the same object.

[ueshin]

identical and equals should be True for the comparison between the same object.

>>> import pandas as pd
>>> idx = pd.Index(['a', 'b', 'c'])
>>> midx = pd.MultiIndex.from_tuples([('a', 'x'), ('b', 'y'), ('c', 'z')])
>>> midx.names = ("nameA", "nameB")

>>> idx.identical(idx)
True
>>> midx.identical(midx)
True

>>> idx.equals(idx)
True
>>> midx.equals(midx)
True

[codecov-io]

Codecov Report

Merging #1220 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1220   +/-   ##
======================================
  Coverage    95.2%   95.2%           
======================================
  Files          35      35           
  Lines        7257    7257           
======================================
  Hits         6909    6909           
  Misses        348     348

Impacted Files	Coverage Δ
databricks/koalas/indexes.py	96% <100%> (ø)	⬆️

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[HyukjinKwon]

Oops, thanks for fixing this. @ueshin.