change ConwayPolynomials package to use flint

The flint library contains the list of Conway polynomials, so we
can delete our copy of it and start using flint to get the polynomials.
Merge branch 'linalg' of github.com:MikeStillman/M2 into linalg
Merge pull request #22 from DanGrayson/linalg

change ConwayPolynomials package to use flint