Implements hook_uninstall()

implements_hook_uninstall.php

<?php
/**
 * Implements hook_uninstall().
 */
function drupal_way_test_uninstall() {
  // Remove the all module tables.
  drupal_uninstall_schema('drupal_way_test');
  // Remove the all module variables.
  // variable_del('drupal_way_test_...');
  // variable_del('drupal_way_test_...');
  // variable_del('...');
  // Or.
  $variables = db_select('variable', 'v')
    ->fields('v', array('name'))
    ->condition('v.name', db_like('drupal_way_test_') . '%', 'LIKE')
    ->execute()
    ->fetchAllAssoc('name');

  if (!empty($variables)) {
    global $conf;
    $variables = array_keys($variables);

    foreach ($variables as $variable_name) {
      db_delete('variable')
        ->condition('name', $variable_name)
        ->execute();

      unset($conf[$variable_name]);
    }
    // Variable cache clear.
    cache_clear_all('variables', 'cache_bootstrap');
  }
}