chore(dependency): remove six library

[bednar]

Proposed Changes

Removed six library which is a Python 2 and 3 compatibility library.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• pytest tests completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #439 (fc66b9f) into master (e46b810) will decrease coverage by 0.02%.
The diff coverage is 80.64%.

@@            Coverage Diff             @@
##           master     #439      +/-   ##
==========================================
- Coverage   89.35%   89.32%   -0.03%     
==========================================
  Files          38       38              
  Lines        3249     3242       -7     
==========================================
- Hits         2903     2896       -7     
  Misses        346      346              

Impacted Files	Coverage Δ
influxdb_client/_async/api_client.py	51.25% <66.66%> (-0.18%)	⬇️
influxdb_client/_sync/api_client.py	73.11% <77.77%> (-0.10%)	⬇️
influxdb_client/configuration.py	87.77% <83.33%> (-0.14%)	⬇️
influxdb_client/_async/rest.py	78.04% <100.00%> (-0.18%)	⬇️
influxdb_client/_sync/rest.py	85.58% <100.00%> (-0.26%)	⬇️
influxdb_client/client/write/point.py	96.71% <100.00%> (-0.03%)	⬇️

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[rhajek]

LGTM