Remove unused variable (matrix_bot_matrix_registration_environment_variables_extension)

roles/custom/matrix-bot-matrix-registration-bot/defaults/main.yml

@@ -33,7 +33,6 @@ matrix_bot_matrix_registration_bot_api_token: ''
 matrix_bot_matrix_registration_bot_device_id: "matrix-docker-ansible-deploy"
 
 matrix_bot_matrix_registration_bot_logging_level: info
-matrix_bot_matrix_registration_environment_variables_extension: ''
 
 matrix_bot_matrix_registration_bot_container_network: ""