[commit-patch-buffer.el] Rearrange names and get rid of now pointless function.

There are now just 2 functions:

commit-patch-buffer - Fully automatic, takes no arguments (bound to C-c C-c).
commit-patch-buffer-manually - Takes 2 interactive arguments.

Dropped commit-patch-current-buffer which took just a directory argument as
it seems pointless now--use commit-patch-buffer-manually instead.