chore: revert feat(enterprise/coderd): allow system users to be added to groups (#19254)

This reverts commit b200fc8e67
(https://github.com/coder/coder/pull/18341).

coderd/database/dbauthz/dbauthz.go

@@ -485,16 +485,6 @@ var (
 					rbac.ResourceFile.Type: {
 						policy.ActionRead,
 					},
-					// Needs to be able to add the prebuilds system user to the "prebuilds" group in each organization that needs prebuilt workspaces
-					// so that prebuilt workspaces can be scheduled and owned in those organizations.
-					rbac.ResourceGroup.Type: {
-						policy.ActionRead,
-						policy.ActionCreate,
-						policy.ActionUpdate,
-					},
-					rbac.ResourceGroupMember.Type: {
-						policy.ActionRead,
-					},
 				}),
 			},
 		}),