[timed] Remove half-implemented filter state that tracks network

Remove state_flt_conn to cut down the complexity of the timed
state machine.

The state state_flt_conn filters events based on whether a network
connection is available. However, timed has no public API for
enabling network tracking in events.

Removing the state will not affect existing alarms, which could
not use the feature because of missing API.
Merge pull request #49 from pgerdt/remove-obsolete-state

[timed] Remove half-implemented filter state that tracks network