chore: sil_senegal and sil_cameroon lexical models should be under sil_senegal/ and sil_cameroon/

[mcdurdin]

Currently, this is not enforced in the build scripts but we have used some scripts in the past which assume that the prefix will match

So: release/sil/sil_cameroon.mct.mengisa should be release/sil_cameroon/sil_cameroon.mct.mengisa.

And so on.

This should not require a version bump as it is internal to the repo.

I have not checked all the other paths.