Removed escape workaround for png exports of HTML models

[philippjfr]

No longer needed and messed up HTML exports in certain scenarios.

[codecov]

Codecov Report

Merging #1206 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1206      +/-   ##
==========================================
- Coverage   87.63%   87.62%   -0.02%     
==========================================
  Files         106      106              
  Lines       12588    12553      -35     
==========================================
- Hits        11031    10999      -32     
+ Misses       1557     1554       -3     

Impacted Files	Coverage Δ
panel/io/state.py	90.00% <ø> (-0.20%)	⬇️
panel/io/save.py	74.50% <100.00%> (-7.93%)	⬇️
panel/util.py	86.09% <100.00%> (+0.90%)	⬆️

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