data provider: remove default admin

you need to load initial data or set "create_default_admin" to true
and the appropriate env vars if you don't want to use the web admin
setup screen to create the default admin

ftpd/ftpd_test.go

@@ -254,6 +254,8 @@ func TestMain(m *testing.M) {
 	// work in non atomic mode too
 	os.Setenv("SFTPGO_COMMON__UPLOAD_MODE", "2")
 	os.Setenv("SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN", "1")
+	os.Setenv("SFTPGO_DEFAULT_ADMIN_USERNAME", "admin")
+	os.Setenv("SFTPGO_DEFAULT_ADMIN_PASSWORD", "password")
 	err = config.LoadConfig(configDir, "")
 	if err != nil {
 		logger.ErrorToConsole("error loading configuration: %v", err)