ada: Drop vxworks-smp-ppc-link.spec

Adding -msmp to linker options in system-vxworks-ppc-rtp-smp.ads
obviated vxworks-smp-ppc-link.spec.  Drop it.

gcc/ada/ChangeLog:

	* libgnat/system-vxworks-ppc-rtp-smp.ads: Drop
	--specs=vxworks-ppc-link.spec from Linker_Options.
	* vxworks-smp-ppc-link.spec: Delete.