dev-libs/ppl: drop to ~arm64

Only sci-mathematics/polymake uses this, and we don't have that even
~arm64 keyworded, so drop unnecessary ppl from stable instead of
catching up in version with other architectures.

Package-Manager: Portage-2.3.28, Repoman-2.3.9

dev-libs/ppl/ppl-1.1.ebuild

@@ -9,7 +9,7 @@ SRC_URI="http://bugseng.com/products/ppl/download/ftp/releases/${PV}/${P}.tar.xz
 
 LICENSE="GPL-3"
 SLOT="0/4.13" # SONAMEs
-KEYWORDS="alpha amd64 arm arm64 hppa ia64 m68k ~mips ppc ppc64 s390 sh sparc x86 ~amd64-fbsd ~x86-fbsd ~amd64-linux ~sparc-solaris"
+KEYWORDS="alpha amd64 arm ~arm64 hppa ia64 m68k ~mips ppc ppc64 s390 sh sparc x86 ~amd64-fbsd ~x86-fbsd ~amd64-linux ~sparc-solaris"
 IUSE="+cxx doc lpsol pch static-libs test"
 
 RDEPEND=">=dev-libs/gmp-6[cxx]