games-fps/xonotic: Drop mention of media-libs/libtxc_dxtn

Bug: https://bugs.gentoo.org/654468

games-fps/xonotic/xonotic-0.8.2.ebuild

@@ -111,8 +111,3 @@ src_install() {
 	insinto "/usr/share/${PN}"
 	doins -r key_0.d0pk server data
 }
-
-pkg_postinst() {
-	elog "If you are using opensource drivers you should consider installing: "
-	elog "    media-libs/libtxc_dxtn"
-}