chore: remove unused NuGet package Uno.SourceGenerationTasks

[Soap-141]

GitHub Issue: #

Proposed Changes

• Bug fix
• Feature
• Code style update (formatting)
• Refactoring (no functional changes, no api changes)
• Build or CI related changes
• Documentation content changes
• Other, please describe:

Description

Uno.SourceGenerationTasks is not referenced anymore for WinUI.

Impact on version

• Major (Public API was modified.)
  • Public constructs (class, struct, delegate, enum, etc.) were removed or renamed.
  • Public members were removed or renamed.
  • Public method signatures were changed or renamed.
• Minor (Public API was extended.)
  • Public constructs, members, or overloads were added.
• Patch (Public API was unchanged.)
  • A bug in behavior was fixed.
  • Documentation was changed.
• None (The library is unchanged.)
  • Only code under the build folder was changed.
  • Only code under the .github folder was changed.

PR Checklist

• Your conventional commits are aligned with the Impact on version section.
• Documentation is up to date.
  • Content of README.md is up to date.
  • XML documentation is up to date.
• The BREAKING_CHANGES.md document is up to date.
  • Create a new Major.0.0 header if you do a Major change and list the breaking changes.
• Tested on all relevant platforms

Other information

Internal Issue (If applicable):