tailcfg: remove ancient UserProfiles.Roles field

And add omitempty to the ProfilePicURL too while here. Plenty
of users (and tagged devices) don't have profile pics.

Updates #14988

Change-Id: I6534bc14edb58fe1034d2d35ae2395f09fd7dd0d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tailcfg/tailcfg_test.go

@@ -10,7 +10,6 @@ import (
 	"reflect"
 	"regexp"
 	"strconv"
-	"strings"
 	"testing"
 	"time"
 
@@ -649,28 +648,6 @@ func TestCloneNode(t *testing.T) {
 	}
 }
 
-func TestUserProfileJSONMarshalForMac(t *testing.T) {
-	// Old macOS clients had a bug where they required
-	// UserProfile.Roles to be non-null. Lock that in
-	// 1.0.x/1.2.x clients are gone in the wild.
-	// See mac commit 0242c08a2ca496958027db1208f44251bff8488b (Sep 30).
-	// It was fixed in at least 1.4.x, and perhaps 1.2.x.
-	j, err := json.Marshal(UserProfile{})
-	if err != nil {
-		t.Fatal(err)
-	}
-	const wantSub = `"Roles":[]`
-	if !strings.Contains(string(j), wantSub) {
-		t.Fatalf("didn't contain %#q; got: %s", wantSub, j)
-	}
-
-	// And back:
-	var up UserProfile
-	if err := json.Unmarshal(j, &up); err != nil {
-		t.Fatalf("Unmarshal: %v", err)
-	}
-}
-
 func TestEndpointTypeMarshal(t *testing.T) {
 	eps := []EndpointType{
 		EndpointUnknownType,