[TASK] Drop THIS_CID

PageTsConfig can be configured to manipulate some queries in
the backend using marker based logic. One marker is THIS_CID
which refers to a record with field 'cid'. This field exists
nowhere and never did. The code dates back straight to Kaspers
initial subversion commit.
The only reference to this field is a german blog post stating
no further information can be found about this undocumented
feature.
Drop it.

Resolves: #68598
Releases: master
Change-Id: If2bea39cf2311051b893e71028702871c13ca771
Reviewed-on: http://review.typo3.org/42068


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>