Manually starting `cosmic-panel` was not working properly in release
builds, because without `cfg!(debug_assertions)`, the `privileged` flag
wasn't sent on the panel, so it couldn't be propagated to the applets,
which also fail the `client_has_no_security_context()` check.
I don't see a way to have both the `cfg!(debug_assertions)` check and
`COSMIC_ENABLE_WAYLAND_SECURITY`. Now only the latter is used, and it
determines the value of `privileged` for clients started normally. In
the future, we could make the default value of
`COSMIC_ENABLE_WAYLAND_SECURITY` depend on `cfg!(debug_assertions)` if
desired.
This also corrects the inconsistency that the `cfg!(debug_assertions)`
check wasn't applied to the render-node-specific Wayland sockets.
