Drop Phing for Makefile

[Kocal]

See phpstan/phpstan-symfony#160

[ondrejmirtes]

So the work remaining is:

• phpstan-mockery
• phpstan-nette
• phpdoc-parser https://github.com/phpstan/phpdoc-parser

Additionally, if you feel like it, it would be great if all extensions got the following improvements:

• Run PHPCS on PHP 8
• Downgrade PHPUnit on older PHP versions instead of upgrading it on newer PHP versions. This is so that extensions can be developed on newer PHP versions out of the box. See how I did it in phpstan-src: phpstan/phpstan-src@8db956f#diff-d2ab9925cad7eac58e0ff4cc0d251a937ecf49e4b6bf57f8b95aab76648a9d34 (the work will be easier in extensions because they don't use paratest)

[Kocal]

Alright, I think I would be able to work on it monday or tuesday.