kio_trash: remove unnecessarily strict permission check

Tested with `chmod 0770 /d/.Trash-1000` (where /d is a mount point),
kio_trash complained about security checks before this commit,
and works with it.

Also tested with a USB key which ends up mounted as
type vfat (rw,nosuid,nodev,relatime,uid=1000,gid=100,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,showexec,utf8,flush,errors=remount-ro,uhelper=udisks2). After kio_trash creates .Trash-1000
it complained about a "strange filesystem", and while this is still true :),
the removal of the code in TrashImpl::initTrashDirectory makes
the trash dir on the USB key usable.

BUG: 76380
FIXED-IN: 5.74