Dependencies: Remove Percy

[amotl]

Percy should actually be pulled in appropriately by dash[testing], right? So, it should do no harm removing the direct dependency to percy-selenium here. CI may prove me wrong ;].

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (7162ddf) 89.69% compared to head (0c1de60) 89.70%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1033      +/-   ##
==========================================
+ Coverage   89.69%   89.70%   +0.01%     
==========================================
  Files         103      103              
  Lines        9497     9497              
  Branches     1056     1056              
==========================================
+ Hits         8518     8519       +1     
+ Misses        765      764       -1     
  Partials      214      214              

Flag	Coverage Δ
unittests	89.70% <ø> (+0.01%)	⬆️

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see 1 file with indirect coverage changes

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