x11-misc/pcmanfm: fix double KEYWORDS

Double KEYWORDS lines break tools like ekeyword and Nattka.
As per PMS, blank/empty KEYWORDS is implied by not defining
the variable.

See: https://projects.gentoo.org/qa/policy-guide/ebuild-format.html#pg0105
Package-Manager: Portage-3.0.14, Repoman-3.0.2
Signed-off-by: Sam James <sam@gentoo.org>

x11-misc/pcmanfm/pcmanfm-9999.ebuild

@@ -1,4 +1,4 @@
-# Copyright 1999-2018 Gentoo Foundation
+# Copyright 1999-2021 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=6
@@ -13,7 +13,6 @@ inherit autotools eutils xdg-utils l10n readme.gentoo-r1
 if [[ ${PV} == *9999* ]]; then
 	EGIT_REPO_URI="git://git.lxde.org/git/lxde/${PN}"
 	inherit git-r3
-	KEYWORDS=""
 else
 	SRC_URI="mirror://sourceforge/${PN}/${P}.tar.xz"
 	KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~mips ~ppc ~x86"