Removed maybe type from metric payload.

The connect and disconnect payloads were previously using a maybe
type of an array of unsigned bytes to contain a UUID. The maybe
type is not handled by DBUS, and thus was causing these metrics
to not be reported.

The solution was to remove the maybe type from this, as a value of
NULL for an array is already an acceptable value to g_variant_new().
Semantically, it indicates an empty array in the GVariant world.

Both Event UUIDs had to be changed with this fix to correctly associate
some old "dev" metrics that were generated outside of the actual code path
but had the previous Event UUIDs. These new UUIDs will be documented
in the online wiki entry.
[endlessm/eos-sdk#2280]