package/rpm: bump to version 4.15.1

- Drop both patches (already in version)
- Add libgcrypt optional dependency (added in version 4.15.1 with
  https://github.com/rpm-software-management/rpm/commit/037106ecc899bad6d6e6f9d95768699542b871ea)
- Add openmp support (added in version 4.15.1 with
  https://github.com/rpm-software-management/rpm/commit/464d21dc8c176222c6586e2ee503fec6207f0d29

)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>