Collapse down to 1 time format for packet headers (missions can customize msg module for alternates)

[skliper]

Is your feature request related to a problem? Please describe.
#726 made it possible to replace header implementation such that the core no longer needs to carry mission unique logic. It also added the single time format implementation, but did not switch to use it by default to minimize functional changes from that PR.

Describe the solution you'd like
Clean/remove all references to CFE_MISSION_SB_PACKET_TIME_FORMAT. Note the change in #726 also fixes #92 when the new implementation is chosen. Now just will do big endian, 6 byte sub-second field.

Describe alternatives you've considered
N/A

Additional context
#726

Requester Info
Jacob Hageman - NASA/GSFC