Clean up project settings

[dotMorten]

Summary of the pull request

• Combine DISABLE_XAML_GENERERATED_MAIN constant into a single setting, and ensure any other constants aren't overwritten.
• Remove explicit build actions that are default already,

References and relevant issues

Detailed description of the pull request / Additional comments

Just cleans the devhome project up a little by removing extra settings not needed.

Validation steps performed

Functional testing of application and explicitly tested the files and settings that were touched.

PR checklist

• [ ] Closes #xxx
• [ ] Tests added/passed
• [ ] Documentation updated

[EricJohnson327]

/azp run

[azure-pipelines[bot]]

No pipelines are associated with this pull request.

[crutkas]

seeing if i can't get the new system to trigger. I'm going to have to close and reopen this