fix: memory leak on WPF

[glennawatson]

What kind of change does this PR introduce?

fixes #2935

What is the current behavior?

There is a memory leak introduced in #2793

What is the new behavior?

Remove the dispatcher object hook to prevent the memory leak.

What might this PR break?

Users relying on the dispatcher closing, but this will cause a memory leak which is the greater evil.

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

[codecov]

Codecov Report

Merging #2986 (72004d8) into main (aa50420) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2986      +/-   ##
==========================================
- Coverage   72.20%   72.14%   -0.07%     
==========================================
  Files         140      140              
  Lines        4904     4893      -11     
==========================================
- Hits         3541     3530      -11     
  Misses       1363     1363              

Impacted Files	Coverage Δ
src/ReactiveUI.Wpf/ActivationForViewFetcher.cs	97.72% <ø> (-0.46%)	⬇️

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[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.