Build/Test Tools: Update the `grunt clean` task after [61438].

The list of files cleaned through `grunt clean` was not updated as part of [61438]. This results in files persisting within `src/wp-includes` even after= they are removed.

Props jorbin.
Fixes #64716. See #64393.

git-svn-id: https://develop.svn.wordpress.org/trunk@62051 602fd350-edb4-49c9-b593-d223f7449a82