ibm_emac: Remove the ibm_emac driver

The arch/ppc sub-tree has been removed in the powerpc git tree.  The old
ibm_emac driver is no longer used by anything as a result of this.  This
removes it, leaving the ibm_newemac driver as the proper driver to use for
PowerPC boards with the EMAC hardware.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>