Remove commented-out "support" for perl's malloc with x2p.

Remove commented-out "support" for perl's malloc with x2p.

In 1998 commit 30e2e4257067d5f8 stated

    temporarily disable perl malloc for a2p until we clean up
    conflicting malloc() declarations everywhere

and nothing has changed since. 13 years later, no-one has reported problems,
so it's safe to remove it.