The "Delete this build" buttons on build pages and also the "Delete this build and all configurations of this build" buttons on matrix build pages
should be converted to links in the sidepanel of the respective pages (see Screenshots).

This simplifies the user experience of deleting an object (see the "Delete Project" link in the sidepanel of project pages).
Having the links in the sidepanel also makes them accessible through the newly added context menus that came with the breadcrumbs.

Recent discussion about this topic:
https://github.com/jenkinsci/jenkins/pull/403