Our implementation of vfs.CheckDeleteSticky was not consistent with Linux,
specifically not consistent with fs/linux.h:check_sticky().
One of the biggest differences was that the vfs implementation did not
allow the owner of the sticky directory to delete files inside it that belonged
to other users.
This change makes our implementation consistent with Linux.
Also adds an integration test to check for this. This bug is also present in
VFS1.
Updates #3027
PiperOrigin-RevId: 355557425
Ayush Ranjan