sysutils/uefi-edk2-bhyve*: Update and migrate to Python 3
- remove dependency on the now obsolete Python 2.7.
- sysutils/uefi-edk2-bhyve now uses the GH/tianocore/edk2 upstream repo.
- sysutils/uefi-edk2-bhyve-csm is no longer a slave port, since it continues to use the GH/freebsd/uefi-edk2 repo.
- sysutils/uefi-edk2-bhyve-devel is no longer required, so delete it.
- Update the port Makefiles to follow the style in sysutils/edk2.