break the old private versions

the way we handled transitioning is entirely garbage.
if libkdecorations2private(N-1) and libkdecorations2privateN are
installed
at the same then clearly one of the dependees of the private ABI has not
been rebuilt yet. so we must have the new lib break the old lib to force
its removal (or the upgrade getting held) otherwise the system is only
half transitoned and falls into ABI holes

e.g. bug 437975 which I'm sure is happening because the gtk style thing
hadn't been rebuilt for the new ABI and thus getting a nullptr where it
should be getting something meaningful. and the only reason that went by
undetected is because the system is perfectly happy with v8 and v9 being
installed at the same time. them being private ABI we cannot allow this,
ever, on principal. it will lead to situations where a dependee wants
private8 but the library wants private9 when that situations is allowed
we now have to different versions of the same library loaded.