The powerpc e500 port has been LTS'd

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* libgnat/system-vxworks7-e500-kernel.ads: Remove.
	* libgnat/system-vxworks7-e500-rtp-smp.ads: Likewise.
	* libgnat/system-vxworks7-e500-rtp.ads: Likewise.