libtraceevent: Fix build with binutils 2.35

In binutils 2.35, 'nm -D' changed to show symbol versions along with
symbol names, with the usual @@ separator.  When generating
libtraceevent-dynamic-list we need just the names, so strip off the
version suffix if present.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Tested-by: Salvatore Bonaccorso <carnil@debian.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-trace-devel@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>