(core) Remove the old attempt at ACLs implemented in Python.

Summary:
The new plans for granular access control are different and handled by
node.js. Some of the same tables will be reused, of which we never made
real use before except for expecting certain specific initial records.

This diff removes the old logic, replacing it with a stub that satisfies
the interface expected by other code.

It also removes several unused UserActions: AddUser/RemoveUser/
AddInstance/RemoveInstance.

Test Plan: Existing tests should pass.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2662

app/server/lib/ActiveDoc.ts

@@ -790,8 +790,7 @@ export class ActiveDoc extends EventEmitter {
   }
 
   public async removeInstanceFromDoc(docSession: DocSession): Promise<void> {
-    const instanceId = await this._sharing.removeInstanceFromDoc();
-    await this._applyUserActions(docSession, [['RemoveInstance', instanceId]]);
+    await this._sharing.removeInstanceFromDoc();
   }
 
   public async renameDocTo(docSession: OptDocSession, newName: string): Promise<void> {

app/server/lib/GranularAccess.ts

@@ -42,10 +42,7 @@ const SPECIAL_ACTIONS = new Set(['InitNewDoc',
                                 ]);
 
 // Odd-ball actions marked as deprecated or which seem unlikely to be used.
-const SURPRISING_ACTIONS = new Set(['AddUser',
-                                    'RemoveUser',
-                                    'AddInstance',
-                                    'RemoveInstance',
+const SURPRISING_ACTIONS = new Set([
                                     'RemoveView',
                                     'AddViewSection',
                                    ]);