Remove Down Vote Button and Obsolete UI command

[QilongTang]

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Purpose

DYN-1990
As a Dynamo dev, I want to clean up package down vote info to push positive reinforcement.

Before:

After:

Declarations

Check these if you believe they are true

• The code base 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.
  Running Self CI
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning, and are documented in the API Changes document.

Reviewers

@DynamoDS/dynamo

FYIs

@Dewb @johnpierson @Amoursol

[mjkkirschner]

if someone calls this method - it should do nothing right? Will the continuation ever get called?

[QilongTang]

Yes, since the handler of the DownvoteRequested event is removed, the call will do nothing and return nothing

[QilongTang]

Self CI passed

[mjkkirschner]

@QilongTang LGTM