unparam lint (#16771)

* fixed: `identifier` is unused lint error

* make saveMultipleMembersT method saveMultipleMembers

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/plugin_api_tests/test_send_mail_plugin/main.go

@@ -25,7 +25,7 @@ func (p *MyPlugin) OnConfigurationChange() error {
 	return nil
 }
 
-func (p *MyPlugin) MessageWillBePosted(c *plugin.Context, post *model.Post) (*model.Post, string) {
+func (p *MyPlugin) MessageWillBePosted(_ *plugin.Context, _ *model.Post) (*model.Post, string) {
 	to := p.configuration.BasicUserEmail
 	subject := "testing plugin api sending email"
 	body := "this is a test."