remove() {
    if (this.to && this.to.incomingInlineRelation === this) {
      this.to.incomingInlineRelation = undefined;
    }
    this.from.removeRelation(this);
    return this;
  }
Removes the relation from the graph it's currently part
of. Doesn't detach the relation (compare with
[`relation.detach()`]{@link Relation#detach}).

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