tools/runqslower: Remove tools/lib/bpf from include path

Since we are now consistently using the bpf/ prefix on #include directives,
we don't need to include tools/lib/bpf in the include path. Remove it to
make sure we don't inadvertently introduce new includes without the prefix.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157952561027.1683545.1976265477926794138.stgit@toke.dk