Remove --testdox parameter from phpunit command

The `--testdox` parameter replaces the printer we previously set with `--printer`.

This causes the following problems:
- The previous exception is not shown, see sebastianbergmann/phpunit#5863
- The "HTML output was generated" message from Drupal is not shown.

By removing the argument we fall back to the Drupal output printer. A developer can still manually append --testdox when running `ddev phpunit`.

commands/web/phpunit

@@ -18,5 +18,5 @@ if [ -f "phpunit.xml" ]; then
     phpunit "$@"
 else
     # Bootstrap Drupal tests and run all custom module tests.
-    phpunit --printer="\Drupal\Tests\Listeners\HtmlOutputPrinter" --bootstrap $PWD/$DDEV_DOCROOT/core/tests/bootstrap.php --testdox $DDEV_DOCROOT/modules/custom "$@"
+    phpunit --printer="\Drupal\Tests\Listeners\HtmlOutputPrinter" --bootstrap $PWD/$DDEV_DOCROOT/core/tests/bootstrap.php $DDEV_DOCROOT/modules/custom "$@"
 fi