[perl #113812] Always use find_runcv when cloning a sub

[perl #113812] Always use find_runcv when cloning a sub

A closure prototype’s CvOUTSIDE pointer might have been modified if
its containing sub is freed first.  When a sub is cloned, the enclos-
ing sub is always the currently-running sub (not so for formats).

So this commit makes subs always use find_runcv, the way they did
before 71f882da828.

So the closure logic which was needed for formats is now moved into an
else branch that is used only for them.