MM-10731 Revert site url kill server (#8877)

* Revert "MM-9983 Requiring SiteURL to be set. (#8769)"

This reverts commit 0432f995ec.

* Add log message for SiteURL not being set.

model/config_test.go

@@ -82,13 +82,6 @@ func TestConfigDefaultFileSettingsS3SSE(t *testing.T) {
 	}
 }
 
-func TestConfigDefaultSiteURL(t *testing.T) {
-	c1 := Config{}
-	c1.SetDefaults()
-
-	assert.Equal(t, "", *c1.ServiceSettings.SiteURL, "SiteURL should be empty by default.")
-}
-
 func TestConfigDefaultServiceSettingsExperimentalGroupUnreadChannels(t *testing.T) {
 	c1 := Config{}
 	c1.SetDefaults()