LU-9859 libcfs: remove libcfs_debug_vmsg2

LU-9859 libcfs: remove libcfs_debug_vmsg2

Now that libcfs_debug_vmsg2 has no (external) users, we can remove it.
It is used to implement libcfs_debug_msg(), so simply move
the body of the function (suitably modified) into that one caller.

Linux-commit: d42a3aded317c97594c19995879999428de53c46

Signed-off-by: NeilBrown <neilb@suse.com>
Change-Id: I80d24abcc23a8f6e2f8b995d1337ba5038318d5a
Reviewed-on: https://review.whamcloud.com/35225
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>