Remove unnecessary rect modification in the CanvasGraphics.prototype.beginAnnotation method

[Snuffleupagus]

This code was added in PR #14247, however it appears that it was unnecessary even back then.
Note how the rect variable isn't actually being used after it's been copied/updated inside of the hasOwnCanvas && this.annotationCanvasMap-branch, and it's also not used at the end of the beginAnnotation method.

[Snuffleupagus]

/botio browsertest

[moz-tools-bot]

From: Bot.io (Windows)

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Received

Command cmd_browsertest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.193.163.58:8877/8aa02369251811d/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

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Received

Command cmd_browsertest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.241.84.105:8877/aa5059b23c26ab1/output.txt

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.08%. Comparing base (c2bbde1) to head (7e764c0).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21729      +/-   ##
==========================================
- Coverage   90.09%   90.08%   -0.01%     
==========================================
  Files         264      264              
  Lines       67194    67230      +36     
==========================================
+ Hits        60538    60565      +27     
- Misses       6656     6665       +9     

Flag	Coverage Δ
browsertest	66.35% <ø> (-0.04%)	⬇️
fonttest	8.99% <ø> (ø)
integrationtest	69.28% <ø> (+<0.01%)	⬆️
unittest	58.24% <ø> (-0.03%)	⬇️
unittestcli	56.60% <ø> (-0.04%)	⬇️

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[moz-tools-bot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/aa5059b23c26ab1/output.txt

Total script time: 16.52 mins

• Regression tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

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Success

Full output at http://54.193.163.58:8877/8aa02369251811d/output.txt

Total script time: 23.27 mins

• Regression tests: Passed

[Snuffleupagus]

Rebasing to master, no code changes made.