Add Higher-Level Component Deletion to Core

[iamrecursion]

Summary

Now that #484 allows the removal of components from the graph, we need to wrap this functionality in higher-level functions that use this sensibly while maintaining the invariants of core.

Value

We can remove nodes and links from the core graph.

Specification

• Add a deleteLink function that takes a link and removes it from the graph. It will need to take care to handle any references to that link properly, and decide on a well-specified semantics for deleting an in-use link.
• Add a deleteNode function that takes a node and removes it from the graph. It will need to take care to handle any reference to that node (via links and parents), and decide on a well-specified semantics for deleting an in-use link.

Acceptance Criteria & Test Cases

• The above functions have been implemented and are well-tested.