Allow system_server to delete directories in preloads

avc: denied { rmdir } for name="apps" dev="sda35" ino=38 scontext=u:r:system_server:s0 tcontext=u:object_r:preloads_data_file:s0 tclass=dir permissive=0
avc: denied { rmdir } for name="demo" dev="sda35" ino=41 scontext=u:r:system_server:s0 tcontext=u:object_r:preloads_data_file:s0 tclass=dir permissive=0

Bug: 28855287
Change-Id: Ia470f94d1d960cc4ebe68cb364b8425418acdbd4