Revert "sci-mathematics/agda-stdlib: Install agda-lib-ffi"

This reverts commit 4ba7508e4abac2adfffb28abf9947751006a3303.
New ebuild for sci-mathematics/agda-lib-ffi

This package installs the haskell modules required for compiling agda
programs using the MAlonzo haskell backend.
Add agda-lib-ffi as runtime dependency

It is controlled by the ffi useflag and is enabled by default.
Merge pull request #285 from vikraman/agda-stdlib_ffi

sci-mathematics/agda-lib-ffi - Neat, thanks!  Sorry for the delay, I didn't notice the pull request earlier.  I will also push your change to portage, your earlier change is already in portage, so I will have to bump the revision.