refact(billing): Use sql functions instead of views

These functions will ensure that UTC time is used for billing queries,
eliminating the need for the repository to set the timezone. This also
means the repository no longern needs a writer.

internal/daemon/controller/controller.go

@@ -451,7 +451,7 @@ func New(ctx context.Context, conf *Config) (*Controller, error) {
 		return server.NewRepositoryStorage(ctx, dbase, dbase, c.kms)
 	}
 	c.BillingRepoFn = func() (*billing.Repository, error) {
-		return billing.NewRepository(ctx, dbase, dbase)
+		return billing.NewRepository(ctx, dbase)
 	}
 
 	// Check that credentials are available at startup, to avoid some harmless