Remove "asssertions" support from libcpp

[Steven Bosscher]

Hi Tom,

Assertions in libcpp have been deprecated since r135264:

2008-05-13  Tom Tromey  <tromey a redhat dot com>

        PR preprocessor/22168:
        * expr.c (eval_token): Warn for use of assertions.

Can this feature be removed for GCC 4.6?

Ciao!
Steven