Issue #3432326 by mondrake: Remove deprecated code from the Extension API

core/.phpstan-baseline.php

core/lib/Drupal/Core/Extension/DatabaseDriverList.php

...rupal/Core/Extension/DatabaseDriverUninstallValidator.php

.../Extension/Discovery/RecursiveExtensionFilterIterator.php

core/lib/Drupal/Core/Extension/Extension.php

core/lib/Drupal/Core/Extension/InfoParser.php

core/lib/Drupal/Core/Extension/InfoParserDynamic.php

core/lib/Drupal/Core/Extension/ModuleInstaller.php

core/lib/Drupal/Core/Extension/ThemeInstaller.php

...ts/Drupal/Tests/Core/Extension/DatabaseDriverListTest.php

...ts/Drupal/Tests/Core/Extension/ExtensionDiscoveryTest.php

.../tests/Drupal/Tests/Core/Extension/InfoParserUnitTest.php

...tests/Drupal/Tests/Core/Extension/LegacyExtensionTest.php