tools: bpf: Fix error in 'make -C tools/ bpf_install'

make[2]: *** No rule to make target 'install'.  Stop.
make[1]: *** [Makefile:122: runqslower_install] Error 2
make: *** [Makefile:116: bpf_install] Error 2

There is no rule for target 'install' in tools/bpf/runqslower/Makefile,
and there is no need to install it, so just remove 'runqslower_install'.

Fixes: 9c01546d ("tools/bpf: Add runqslower tool to tools/bpf")
Signed-off-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210628030409.3459095-1-liwei391@huawei.com