phpPackages: drop all packages and package versions for PHP5

PHP5 will be EOLed by the end of the year: https://secure.php.net/supported-versions.php

In fact we don't support PHP5 anymore since 7e6b76fc.

The following packages had older versions packaged as well to retain
PHP5 support:

* APCu (4.0.11)
* Memcached (2.2.0), Memcache (3.0.8)
* XDebug (2.3.1)
* YAML (1.3.1)
* pthreads (2.0.10)
* redis (2.2.7)

The following packages were removed entirely due to missing support for
PHP7:

* spidermonkey
* zendopcache (part of PHP itself since 5.5)
* xcache
* geoip

Furthermore I declared `phpPackages.pthreads` as broken for now as it
supports PHP7, but the last release was 2016 and therefore PHP 7.0 is
supported, but the build fails with PHP 7.1 and PHP 7.2 (https://pecl.php.net/package/pthreads).