math/clp: Fix file conflicts with math/coin-or-data-sample, math/coin-or-data-netlib, math/coinutils

clp was installing the same files that the above three ports install.
This is because COIN-OR ports are designed to be self-sufficient
and contain and install their own dependencies.

This causes conflicts in the context of a port.

Approved by: portmgr blanket (bugfix)