fs: remove useless lockdep assertion

fs: remove useless lockdep assertion

mnt_ns_release() can run asynchronously via call_rcu() so hitting that
lockdep assertion means someone else already grabbed the
mnt_ns_tree_lock and causes a false positive. That assertion has likely
always been wrong. call_rcu() just makes it more likely to hit.

Link: https://lore.kernel.org/r/Z2PlT5rcRTIhCpft@ly-workstation
Link: https://lore.kernel.org/r/20241219-darben-quietschen-b6e1d80327bb@brauner
Reported-by: Lai, Yi <yi1.lai@linux.intel.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>