Modify javadoc for some extra values of VpnManager event

The underlying network, NetworkCapabilities and LinkProperties
are not necessary to send to VPN app since the purpose of
CATEGORY_EVENT_DEACTIVATED_BY_USER and
CATEGORY_EVENT_ALWAYS_ON_STATE_CHANGED are to notify VPN
app that VPN is deactivated by the user or VPN always-on
status is changed.

Bug: 191413541
Test: Javadoc only changes.
Change-Id: I7fd4b6dad1a4363336f03c217e635fc45bcd0ab6