Drop HHVM support no longer compatible or testable under modern PHP (7.4).

[terabytesoftw]

HHVM has diverged from the PHP language since version 4.0 (2019) and no longer supports PHP syntax or features introduced after PHP 7.1.

Maintaining conditional support for HHVM in Yii2 adds technical debt, and makes it impossible to achieve accurate test coverage especially now that coverage is being raised across the framework.

Removing HHVM references (code checks, and docs) will simplify maintenance, reduce noise in the codebase, and ensure the test suite reflects real PHP environments (7.4 - 8.4).

https://hhvm.com/blog/2018/09/12/end-of-php-support-future-of-hack.html

[samdark]

I'm for removing it.