detach() {
    this.from.markDirty();
    this.remove();
    return this;
  }
Detaches the relation from the asset it is currently attached
to. If the relation is currently part of a graph, it will
removed from it.

Detaching implies that the tag/statement/declaration
representing the relation is physically removed from the
referring asset. Not all relation types support this.

@return {Relation} The relation itself (chaining-friendly).