Revert whence exposure in CAF::FileWriter

This introduces a dependency on perl-List-MoreUtils-0.33, which is not
available on EL6.  This is blocking the release.

We'll reintroduce this feature for 14.6.

This reverts commit 5f890d9918848a0e06dee97c55ccb75b1336ff29, reversing
changes made to db3faa774cb384a2203cab28d9f990bf841a4a99.