Remove transport part of the RSS module

• User impact:

  Low
• Effort points:

  0.5
• Affects Docs:

  Yes
• Migration Impact:

  Deprecate the RSS transport (i.e. in schema) and remove in 3.2.0
• Similar Issues:

  None

Despite being a module, there are still transport parts in the RSS Maven module: RssEndpointBuilder, RssInboundEndpoint and friends.

IMHO RSS is a pure payload handling module and should not contain any transport parts.