filter_libc: remove the line holding the futex syscall error entirely

filter_libc: remove the line holding the futex syscall error entirely

The current filter might leave empty lines behind.
This is caused by the fact that glibc used to not include a newline
in the message. But since glibc 2.29 it does.

https://bugs.kde.org/show_bug.cgi?id=405205
Reported-by: Stefan Maksimovic <stefan.maksimovic@rt-rk.com>