[Feature Request] Delete unused feature branch

[filzrev]

Is your feature request related to a problem? Please describe.
Delete feature/watch branch from docfx repository.
Because that using pull_request_target trigger.

Additional context
When PR's target branch is feature/watch.
It seems pull_request_target trigger is used.

It is possible that it cause vulnerable when used on a public repository.
(Related PR: #10673)