Feature summary: Provide a button to clear deletion reason when performing deletion action.

Use case(s):
When trying to delete a page via dropdown menu or via direct link, there will appear an autofilled deletion reason looks like content was: "[redacted]...", and the only contributor was "[redacted]. It somehow provide a preview for normal users who are curious about the content of that deleted page, but it could also messed up deletion log and cause the leakage of something inappropriate.
Admins among Wikimedia projects has used script like this for a pretty long period, and I thought it make sense to integrate this feature into core codebase. Despite a abrupt clear of autofilled reason, I think it is a better approach to provide a button which could clear the reason once it is clicked.

Benefits :
Beneficial for those admins which are lazy but want a clear deletion log.