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/httpmw/ratelimit.go

@@ -47,7 +47,7 @@ func RateLimit(count int, window time.Duration) func(http.Handler) http.Handler
 
 			// We avoid using rbac.Authorizer since rego is CPU-intensive
 			// and undermines the DoS-prevention goal of the rate limiter.
-			for _, role := range auth.Actor.SafeRoleNames() {
+			for _, role := range auth.SafeRoleNames() {
 				if role == rbac.RoleOwner() {
 					// HACK: use a random key each time to
 					// de facto disable rate limiting. The