Remove obsolte ebuild

It's old and unmaintained, and there is an official one now:

c18ea60fb1

Signed-off-by: Conrad Hoffmann <ch@bitfehler.net>

gentoo/app-metrics/smartctl_exporter/files/smartctl_exporter.yaml

@@ -1,7 +0,0 @@
-smartctl_exporter:
-  bind_to: "localhost:9633"
-  url_path: "/metrics"
-  smartctl_location: /usr/sbin/smartctl
-  collect_not_more_than_period: 120s
-  devices:
-  - /dev/sda

gentoo/app-metrics/smartctl_exporter/smartctl_exporter-9999.ebuild

@@ -1,31 +0,0 @@
-# Copyright 2022 The Prometheus Authors
-# Copyright 2019 Maxim "Sheridan" Gorlov
-# Distributed under the terms of the Apache License Version 2.0
-
-EAPI=6
-EGIT_REPO_URI="https://github.com/prometheus-community/${PN}"
-inherit git-r3
-
-DESCRIPTION="Exporting S.M.A.R.T. metrics"
-HOMEPAGE="https://github.com/prometheus-community/smartctl_exporter"
-LICENSE="Apache-2.0"
-SLOT="0"
-RDEPEND="sys-apps/smartmontools"
-DEPEND="dev-lang/go"
-KEYWORDS="~amd64 ~ppc ~x86 ~arm"
-
-src_unpack() {
-        git-r3_src_unpack
-        cd "${S}"
-        make get
-}
-
-src_compile() {
-	make build
-}
-
-src_install() {
-	newbin bin/${PN}-${PV} ${PN}
-	dodoc "README.md"
-        insinto /etc
-}