Currently, we can only perform the following actions for REST API in regards to Build Status:
POST or GET
https://docs.atlassian.com/bitbucket-server/rest/4.0.0/bitbucket-build-rest.html

http://example.com/rest/build-status/1.0/commits/{commitId} [POST, GET]

For more information on setting Build Status for a commit:
https://developer.atlassian.com/server/bitbucket/how-tos/updating-build-status-for-commits/

Suggested Request is to allow DELETE as an action to remove the build status rather than setting a status.