btrfs: locking: remove the recursion handling code

[ Upstream commit 4048daed ]

Now that we're no longer using recursion, rip out all of the supporting
code.  Follow up patches will clean up the callers of these functions.

The extent_buffer::lock_owner is still retained as it allows safety
checks in btrfs_init_new_buffer for the case that the free space cache
is corrupted and we try to allocate a block that we are currently using
and have locked in the path.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: 97e86631 ("btrfs: don't set lock_owner when locking extent buffer for reading")
Signed-off-by: Sasha Levin <sashal@kernel.org>