sysv: bury the broken "quietly truncate the long filenames" logics

It's contrary to the normal semantics, only sysv and adfs try to
do that (on any other filesystem you'll get -ENAMETOOLONG instead
of quiet truncation) and nobody actually uses that - it got
accidentally broken 5 years ago and nobody noticed.  Time to
bury it...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>