[CT-1443] Remove 'root_path' from most node definitions

[gshank]

We are moving towards enabling manifests to be portable. Currently we include the 'root_path' of the project in every node, which is duplicative and non-portable. In addition, this field is hardly used.

Remove root_path from the node class definitions.

Note: because we don't load seed csv file contents, we do use the root_path to load the seed file when the seeds command is run. For now, we will include the root_path in seed nodes, but longer term we need to come up with a solution for this, whether making it possible to get the root_path for every project in the 'load_agate_table' context method or some other solution.

This is done as part of the structured logging effort, as cleanup of the node attributes that need to be included in the contracts for node information.