mptcp: pm: in-kernel: clarify mptcp_pm_remove_anno_addr()

mptcp: pm: in-kernel: clarify mptcp_pm_remove_anno_addr()

The variable 'ret' was used, but it was not cleared what it was, and
probably led to an issue [1].

Rename it to 'announced' to avoid confusions.

While at it, remove the returned value of the helper: it is only used in
one place, and the returned value is not used.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/606
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260205-net-mptcp-misc-fixes-6-19-rc8-v2-2-c2720ce75c34@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>