fsnotify: remove destroy_list from fsnotify_mark

fsnotify: remove destroy_list from fsnotify_mark

destroy_list is used to track marks which still need waiting for srcu
period end before they can be freed.  However by the time mark is added to
destroy_list it isn't in group's list of marks anymore and thus we can
reuse fsnotify_mark->g_list for queueing into destroy_list.  This saves
two pointers for each fsnotify_mark.

Signed-off-by: Jan Kara <[email protected]>
Cc: Eric Paris <[email protected]>
Cc: Heinrich Schuchardt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>