fetchmail: Update to 6.4.19 and using python3

fetchmail: Update to 6.4.19 and using python3

- Update from 6.3.26 (2013-04-23) to 6.4.19 (2021-04-24)
- Update rootfile
- Delete fetchmail-6.3.26-permit-build-without-ssl3.patch as it is not
   needed with version 6.4.19
- Added command to use python3 to lfs
- Changelog is too large to include here
   Full details can be found in NEWS file in the source tarball

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>