Remove VTK_9_PLUS flag

[skoudoro]

Currently, we are depending only on VTK 9.1.0 so this flag is not necessary anymore.

[pep8speaks]

Hello @skoudoro! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2022-01-27 17:33:34 UTC

[codecov]

Codecov Report

Merging #536 (a34c4fe) into master (214375b) will increase coverage by 0.21%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
+ Coverage   81.89%   82.11%   +0.21%     
==========================================
  Files          54       54              
  Lines       10659    10627      -32     
  Branches     1067     1061       -6     
==========================================
- Hits         8729     8726       -3     
+ Misses       1667     1641      -26     
+ Partials      263      260       -3     

Impacted Files	Coverage Δ
fury/fury/tests/test_material.py	11.00% <0.00%> (-1.09%)	⬇️
fury/fury/lib.py	100.00% <0.00%> (ø)
fury/fury/tests/test_deprecator.py	95.67% <0.00%> (+0.02%)	⬆️
fury/fury/material.py	31.34% <0.00%> (+1.34%)	⬆️
fury/fury/utils.py	89.16% <0.00%> (+3.17%)	⬆️
fury/fury/actors/peak.py	94.15% <0.00%> (+4.20%)	⬆️