Issue #3317815 by omkar.podey, tedbow: Remove all fixtures except for one: `fake_site`

...c_updates_extensions/tests/src/Build/ModuleUpdateTest.php

package_manager/tests/fixtures/build_test_projects/README.md

...tures/build_test_projects/alpha/1.0.0/alpha.info.yml.hide

...ts/fixtures/build_test_projects/alpha/1.0.0/composer.json

...tures/build_test_projects/alpha/1.1.0/alpha.info.yml.hide

...ts/fixtures/build_test_projects/alpha/1.1.0/composer.json

...es/build_test_projects/updated_module/1.0.0/composer.json

...rojects/updated_module/1.0.0/updated_module.info.yml.hide

..._test_projects/updated_module/1.0.0/updated_module.module

...es/build_test_projects/updated_module/1.1.0/composer.json

...projects/updated_module/1.1.0/src/PostApplySubscriber.php

...rojects/updated_module/1.1.0/updated_module.info.yml.hide

..._test_projects/updated_module/1.1.0/updated_module.module

...projects/updated_module/1.1.0/updated_module.services.yml

package_manager/tests/src/Build/PackageInstallTest.php

package_manager/tests/src/Build/PackageUpdateTest.php