cells: Delete pcells related classes

Acked-by: Tigran
Target: master, 2.6, 2.10, 2.11
Require-book: no
Require-notes: yes

We removed the remaining pcells classes from the dcache code. There is a separate pcells repo on github now where all the pcells related code can be found. Pcells however has dependencies against the dCache code.

Patch: http://rb.dcache.org/r/7468/