Sunset PHP 7.3

[Lewiscowles1986]

Noticing the FFI PR from @tienvx and my rebase of that branch, both remove PHP 7.3 (makes sense, I don't think it supports FFI, and it's out of all support) #210 See: https://www.php.net/eol.php

In an effort to make that branch smaller, perhaps it is possible to cut a release that deprecates 7.3?

[cfmack]

Resolved