Stop oversampling for HiDPI in annotations editor for full page shots.

[chenba]

Fixes #4268

[codecov-io]

Codecov Report

Merging #4360 into master will decrease coverage by 0.08%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #4360      +/-   ##
==========================================
- Coverage   45.81%   45.72%   -0.09%     
==========================================
  Files          36       36              
  Lines        1600     1603       +3     
  Branches      289      290       +1     
==========================================
  Hits          733      733              
- Misses        867      870       +3

Impacted Files	Coverage Δ
server/src/pages/shot/editor.js	7.04% <0%> (-0.05%)	⬇️

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