mediawiki::packages: place deprecated packages behind lsbdist guard

* php5-wmerrors provides functionality that is built in to HHVM, so we don't
  plan to port it to trusty, ever.
* libmemcached11 is also not packaged for trusty and not required for the
  memcached extension any longer.
* We don't sue php5-igbinary any longer.

Change-Id: If7826798e931c8981e5f529afbeea248556bbb39
Merge "mediawiki::packages: place deprecated packages behind lsbdist guard" into production