Remove the headers for the validity regions pointer analyses

*. These are not built or used by the current develop.
*. pointer_analysis/*_fiv*.cpp were removed long ago so there can't be
   current out-of-tree users.
*. #5020 removed some of these with
   063db53 noting:
   "These are unused in the code base,
    and there are no plans resurrect them."

Author: martin