chore: drop ad-hoc mongodb deps and the throwaway scaffolder

The Behat→PHPUnit migration scaffolder under `tools/` was a one-shot
helper; it has no place in the published source tree.

`doctrine/mongodb-odm` and `doctrine/mongodb-odm-bundle` are installed
on demand by the `mongodb` CI job (and likewise on contributor
machines), not via require-dev — the lines added in #8202 made them
load unconditionally and bloated the install footprint for everyone
else.

Author: soyuka

composer.json

@@ -130,8 +130,6 @@
         "doctrine/common": "^3.2.2",
         "doctrine/dbal": "^4.0",
         "doctrine/doctrine-bundle": "^2.11 || ^3.1",
-        "doctrine/mongodb-odm": "^2.16",
-        "doctrine/mongodb-odm-bundle": "^5.6",
         "doctrine/orm": "^2.17 || ^3.0",
         "elasticsearch/elasticsearch": "^7.17 || ^8.4 || ^9.0",
         "friends-of-behat/mink-browserkit-driver": "^1.3.1",