Skip Dispose() calls in Shutdown()

[QilongTang]

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Purpose

As a follow up of #10672. @mmisol found all Dispose() functions are called twice and I verified that it is indeed the case. So I am removing these dedicated calls to show extension authors that they will only need to implement Dispose() call in the future.

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated

Reviewers

@DynamoDS/dynamo

FYIs

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[mmisol]

Just a minor comment regarding these changes.

We should also update TuneUp and the NodePropertyPalette, right? Any other place we may have documented this? Like a View extension sample?

[mmisol]

Thanks! Looks good to me

[QilongTang]

@mmisol I checked our implementation in https://developer.dynamobim.org/03-Development-Options/3-6-extensions.html and https://github.com/DynamoDS/DynamoSamples/blob/master/src/SampleViewExtension/SampleViewExtension.cs is actually correct. I will make PRs for TuneUp