Remove legacy driver tests and root phpunit config

Remove test files that tested the legacy translator, along with
the test bootstrap, schema helper, and root phpunit.xml.dist.
The new driver tests live in packages/mysql-on-sqlite/.

Removed files:
- tests/WP_SQLite_Translator_Tests.php
- tests/WP_SQLite_Query_Tests.php
- tests/WP_SQLite_Metadata_Tests.php
- tests/WP_SQLite_Query_RewriterTests.php
- tests/WP_SQLite_PDO_User_Defined_Functions_Tests.php
- tests/bootstrap.php
- tests/wp-sqlite-schema.php
- phpunit.xml.dist

Author: JanJakes

composer.json

@@ -42,9 +42,6 @@
 		"prepare-release": [
 			"./bin/prepare-release.sh"
 		],
-		"test": [
-			"phpunit"
-		],
 		"test-e2e": [
 			"@wp-test-ensure-env @no_additional_args",
 			"rm -f tests/e2e/package.json tests/e2e/node_modules @no_additional_args",