#7237: Drop unused webextAlert

[fregante]

What does this PR do?

• Part of Drop vestigial Firefox support #7237
• Related to #7228: Add support for sidePanel in the MV3 build #7354

Discussion

• This alert was only used by Firefox in MV2. I only left it in here because MV3 would have needed it for the sidebar injection
• Since we're going to use the sidePanel, this will become dead code after the sidePanel PR is merged

Future Work

If background alerts ever become needed again, either revert this PR or use https://github.com/fregante/webext-alert

Checklist

• Designate a primary reviewer: @twschiller

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7a5e2e9) 72.52% compared to head (a8e87a9) 72.46%.
Report is 1 commits behind head on main.

❗ Current head a8e87a9 differs from pull request most recent head 155223e. Consider uploading reports for the commit 155223e to get more accurate results

Files	Patch %	Lines
src/background/browserAction.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7384      +/-   ##
==========================================
- Coverage   72.52%   72.46%   -0.06%     
==========================================
  Files        1207     1205       -2     
  Lines       37684    37533     -151     
  Branches     7067     7051      -16     
==========================================
- Hits        27331    27199     -132     
+ Misses      10353    10334      -19     

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[twschiller]

Marking @grahamlangford as primary reviewer. Apologies for accidentally closing - hit the wrong button

[grahamlangford]

See package-lock conflict