selftests: mptcp: pm_nl_ctl: remove re-definition

selftests: mptcp: pm_nl_ctl: remove re-definition

'MPTCP_PM_NAME' is defined in 'linux/mptcp_pm.h', included in
'linux/mptcp.h', no need to re-define it.

'MPTCP_PM_EVENTS' is not defined in 'linux/mptcp.h', but
'MPTCP_PM_EV_GRP_NAME' is, with the same value. We can then use the
latter, and drop the other one.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240902-net-next-mptcp-mib-mpjtx-misc-v1-11-d3e0f3773b90@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>