Avoid applying unintended labels when transferring issues

[jeffhandley]

As @teo-tsirpanis noted in this comment, when issues get transferred from this repository into dotnet/runtime, some unintended labels are getting created in the dotnet/runtime repo. Is this something we can avoid easily?

[teo-tsirpanis]

Issue transfers could be performed by a bot command that first removes labels that don't exist in the target repository.

[performanceautofiler]

Closing because it's stale.