Get rid of the fixed size buffer in VG_(assert_fail). I have no idea
why it was there in the first place. First, we would write into it
and later printf("%s", buf).  We can as well use vprintf directly.
That's what we do now.


git-svn-id: svn://svn.valgrind.org/valgrind/branches/BUF_REMOVAL@14215 a5019735-40e9-0310-863c-91ae7b9d1cf9