filter_xml: Filter out '@*' from <fn> symbol names

filter_xml: Filter out '@*' from <fn> symbol names

With glibc 2.34 we would start seeing some function names ending in
'@*' this was already filtered out using drd/tests/filter_stderr.in
but not when using the drd xml tests. This would make
drd/tests/thread_name_xml and drd/tests/bar_bad_xml fail.

Filter this out in the memcheck/tests/filter_xml script, which is
also used by the drd test filters.

Tested against glibc 2.34, 2.33 and 2.17 on x86_64.