This reverts commit 7d0b699e.

Issue #2927806 by alexpott, mondrake, jibran, Mile23: Use PHPUnit 6 for testing when PHP version >= 7.2

Issue #2578485 by Mile23, mayeco, TamCalderwood, alduya, Gravypower, Andy_D, alexpott, slde_rorschach: Composer::preAutoloadDump fails with no specified classmap

Issue #2764267 by alexpott, Mile23, wengerk, Yogesh Pawar: preAutoloadDump use config composer to determine vendor directory instead of hardcoding

Issue #2851661 by alexpott, dawehner, xjm: Ensure that we're using the right ruleset for coding standards checking

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

Issue #2744463 by Mile23, dawehner, pfrenssen, joelpittet, tstoeckler, alexpott, klausi: Add phpcs, coder 8.2.8 as --dev requirements for drupal/core

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2664274 by alexpott, bojanz, fortis, Mile23, arknoll, Barryvdh: Combination of --prefer-dist and .gitattributes confuses our vendor test cleanup

Issue #2664274 by alexpott, bojanz, fortis, Mile23, arknoll: Combination of --prefer-dist and .gitattributes confuses our vendor test cleanup

Issue #2614764 by snehi, priya.chat, rakesh.gectcr, anil280988, amit.drupal, jhodgdon: Wrong @param doc in class Composer

Issue #2635584 by hussainweb, alexpott: Move core/.gitignore policies to composer events/packaging scripts

Issue #2550519 by klausi, nullkernel, cweagans, alexpott, pwolanin, neclimdul: Crypt::randomBytes() doesn't actually return cryptographically secure random bytes

Issue #2579663 by Mile23, webflo, joshtaylor: Can't use 'composer install' with missing composer.lock and vendor folder

Issue #2600176 by alexpott, dawehner, tim.plunkett: Step 1.875: Include the PhantomJS Mink driver for real

Issue #2592367 by alexpott: PHPUnit is broken - we have dependencies on Symfony event dispatcher tests

Issue #2585165 by pwolanin, alexpott, tarekdj, geertvd, dawehner, greggles: Don't include vendor test code (especially mink) in the Drupal webroot