net: dummy: remove fake SR-IOV functionality

netdevsim driver seems like a better place for fake SR-IOV
functionality.  Remove the code previously added to dummy.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>