Orderer v3: remove support for the system channel

[tock-ibm]

In v3 we will remove support for the system channel.

• Prevent boot with a system channel
• clean up filters
• clean up multi-channel
• clean up consensus
• clean up config tx templating
• clean up the flow for creating a new channel
• clean up the migration path between system-channel usage and channel participation api

In Epic: #3511