chore: merge authorization contexts (#12816)

* chore: merge authorization contexts

Instead of 2 auth contexts from apikey and dbauthz, merge them to
just use dbauthz. It is annoying to have two.

* fixup authorization reference

coderd/users.go

@@ -518,7 +518,7 @@ func (api *API) deleteUser(rw http.ResponseWriter, r *http.Request) {
 	aReq.Old = user
 	defer commitAudit()
 
-	if auth.Actor.ID == user.ID.String() {
+	if auth.ID == user.ID.String() {
 		httpapi.Write(ctx, rw, http.StatusForbidden, codersdk.Response{
 			Message: "You cannot delete yourself!",
 		})