Add project argument to project-kill-buffers

Add project argument to project-kill-buffers

Previously, project-kill-buffers always called (project-current t).  A
Lisp program could change what project project-kill-buffers operated
on by binding project-current-directory-override.  However, in some
edge cases (for example, if the project was deleted between looking it
up and calling project-kill-buffers) this might fail to detect a
project, and so (project-current t) would prompt the user.

To avoid this, accept the project to kill buffers for as an argument.

* lisp/progmodes/project.el (project-kill-buffers): Take project as an
optional argument (bug#72019).

(cherry picked from commit 6b2f51633e0f508d393516d6624e1a4ddaca31d1)