[PATCH v2] malloc: Remove malloc hooks (Bug 23328)

[Florian Weimer]

* Carlos O'Donell:

> For applications that require the hooks the functionality is moved
> entirely to a new shared library: libmalloc-extras.so.  Applications
> should preload libmalloc-extras.so to get back the lost functionality.
> Static applications are not supported, but continue to operate with
> APIs doing nothing or returning errors depending on their semantics.

Usuallly, we remove functionality which is turned into compat symbols
outright.  Why aren't we doing this here?