chore: remove duplicate message field

[usernameisnull]

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Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
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[codecov]

Codecov Report

Base: 47.76% // Head: 47.71% // Decreases project coverage by -0.06% ⚠️

Coverage data is based on head (26fb38b) compared to base (ba86be2).
Patch has no changes to coverable lines.

❗ Current head 26fb38b differs from pull request most recent head e48352f. Consider uploading reports for the commit e48352f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12477      +/-   ##
==========================================
- Coverage   47.76%   47.71%   -0.06%     
==========================================
  Files         246      246              
  Lines       41910    41908       -2     
==========================================
- Hits        20020    19996      -24     
- Misses      19891    19914      +23     
+ Partials     1999     1998       -1     

Impacted Files	Coverage Δ
cmd/argocd/commands/applicationset.go	8.78% <0.00%> (-8.28%)	⬇️
util/webhook/webhook.go	68.28% <0.00%> (-0.11%)	⬇️
util/settings/settings.go	49.36% <0.00%> (ø)
applicationset/services/scm_provider/github.go	81.25% <0.00%> (ø)
applicationset/generators/git.go	86.93% <0.00%> (+0.13%)	⬆️

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[crenshaw-dev]

Thanks, @usernameisnull!