VFS: rename kern_path_locked() and related functions.

kern_path_locked() is now only used to prepare for removing an object
from the filesystem (and that is the only credible reason for wanting a
positive locked dentry).  Thus it corresponds to kern_path_create() and
so should have a corresponding name.

Unfortunately the name "kern_path_create" is somewhat misleading as it
doesn't actually create anything.  The recently added
simple_start_creating() provides a better pattern I believe.  The
"start" can be matched with "end" to bracket the creating or removing.

So this patch changes names:

 kern_path_locked -> start_removing_path
 kern_path_create -> start_creating_path
 user_path_create -> start_creating_user_path
 user_path_locked_at -> start_removing_user_path_at
 done_path_create -> end_creating_path

and also introduces end_removing_path() which is identical to
end_creating_path().

__start_removing_path (which was __kern_path_locked) is enhanced to
call mnt_want_write() for consistency with the start_creating_path().

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Christian Brauner <brauner@kernel.org>