Migrate "User.GetProfilesByUsernames" to Sync by default (#11523)

* changed GetProfilesByUsernames signature

* modified the UserStore interface to reflect changed made to the GetProfilesByUsernames function signature

* modify usages of GetProfilesByUsernames

* fix gofmt

* fixed failing userstore tests

app/user.go

@@ -625,11 +625,11 @@ func (a *App) GetUsersByGroupChannelIds(channelIds []string, asAdmin bool) (map[
 }
 
 func (a *App) GetUsersByUsernames(usernames []string, asAdmin bool, viewRestrictions *model.ViewUsersRestrictions) ([]*model.User, *model.AppError) {
-	result := <-a.Srv.Store.User().GetProfilesByUsernames(usernames, viewRestrictions)
-	if result.Err != nil {
-		return nil, result.Err
+	users, err := a.Srv.Store.User().GetProfilesByUsernames(usernames, viewRestrictions)
+	if err != nil {
+		return nil, err
 	}
-	return a.sanitizeProfiles(result.Data.([]*model.User), asAdmin), nil
+	return a.sanitizeProfiles(users, asAdmin), nil
 }
 
 func (a *App) sanitizeProfiles(users []*model.User, asAdmin bool) []*model.User {