Remove transport part of the Atom module

• User impact:

  Medium
• Effort points:

  0.5
• Affects Docs:

  Yes
• Similar Issues:

  None

Despite being a module, there are still transport parts in the Atom Maven module: AtomEndpointBuilder, AtomInboundEndpoint and friends.

Atom itself is a pure payload format and handling it be in a module only. The transport parts can be removed as they only add maintainance overhead and confusion for end users.