Treesize propagation broken in collaborative mode

[rhafer]

Describe the bug

With WATCH_FS enabled. OpenCloud doesn't correctly account for files being deleted directly from
the filesystem.

Steps to reproduce

1. Start OpenCloud in collaborative mode (STORAGE_USERS_POSIX_WATCH_FS="true")
2. Create files in the personal space of a user:

   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # echo 1234 > test1
   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # echo 1234 > test2 
   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # echo 1234 > test3
   

3. check diskusage and xattrs (looks go so far):

   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # du -bs .
   15      .
   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # xattr -l .                                        
   user.oc.treesize: 15
   ...
   

4. remove a file and check again (the numbers in the xattrs haven't been updated):

   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # rm test3
   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # du -bs .
   10      .
   ~/.opencloud/storage/users/users/056fc874-dd7f-11ef-ba84-af6fca4b7289 # xattr -l .
   user.oc.treesize: 15
   ...