[TASK] Remove igbinary from cache framework

The patch removes igbinary serializer support from the cache framework.
When igbinary support was added back then in PHP 5.3 times, it had the
potential to serialize data quicker than the default serializer.

Unfortunately, other promises aren't held:
* The module found no general acceptance within the PHP community and
  isn't supported very well. PHP 7 is still not officially supported.
* Last release at the time of this writing was in 2014-08
* The module must still be compiled from source and no recent
  distribution ever packaged it by default
* The maintenance load on devOps side is high: The module must be
  recompiled with each minor php release
* In case the module is not updated, it throws errors at a central place
  of the system and can easily brick a whole instance
* The module found no huge acceptance by hosters and is only very rarely
  used in real life instances
* A performance impact is only measurable in very small and highly
  specialized use...