Bug 2177214

Description of problem:
connection.secondaries not updated after secondary connection removal, keeping stale UUID's there

Version-Release number of selected component (if applicable):
NetworkManager-1.42.2-1.el9.x86_64

How reproducible:
always

Steps to Reproduce:
1. have a connection with empty connection.secondaries and an e.g. VPN connection
2. Add VPN connection to base's connection.secondaries
3. delete VPN connection

Actual results:
UUID of a deleted VPN connection is still in base connection's connection.secondaries

Expected results:
UUID of deleted secondary connection is deleted from respective base connections' connection.secondaries entries

Additional info:
Already covered by NMCI scenario connection_secondaries_are_cleared_after_removal in the linked MR.

sort of similar situation is in controller/port connections, however there may be NM users depending on the current behaviour:

$ nmcli c add con-name bond0+ ifname bond0 type bond connection.autoconnect no
Connection 'bond0+' (619ef611-14f1-47e6-92cf-c580727a28dd) successfully added.
$ nmcli c add con-name bond0.10+ ifname eth10 type ethernet connection.autoconnect no master bond0+
Connection 'bond0.10+' (c6f2b280-26f1-42c3-bc50-4f475ee6a819) successfully added.
$ UUID=$(nmcli -g connection.uuid c s bond0+)
$ nmcli -f all c s bond0.10+ | grep "$UUID\|bond0+"
connection.master:                      619ef611-14f1-47e6-92cf-c580727a28dd
$ nmcli c del bond0+
Connection 'bond0+' (619ef611-14f1-47e6-92cf-c580727a28dd) successfully deleted.
$ nmcli -f all c s bond0.10+ | grep "$UUID\|bond0+"
connection.master:                      619ef611-14f1-47e6-92cf-c580727a28dd
$