ci: remove Void Linux CI

This doesn't really seem worth keeping as glibc linux is already covered
by the Arch Linux CI and Void lags behind on package updates enough
compared to the others to be annoying.

.github/workflows/ci_build.yml

@@ -1,79 +0,0 @@
-on:
-  push:
-    branches:
-      - master
-      - '[0-9]+.[0-9]+.x'
-  pull_request:
-    branches:
-      - master
-      - '[0-9]+.[0-9]+.x'
-
-name: voidlinux glibc
-
-jobs:
-  default_build:
-    name: build/test/fmt
-    runs-on: ubuntu-latest
-    container: voidlinux/voidlinux:latest
-
-    steps:
-      - name: install deps
-        run: |
-          xbps-install -Sy xbps
-          xbps-install -Suy
-          # wayland/wlroots dependencies as well as we build from source
-          xbps-install -y MesaLib-devel libseat-devel eudev-libudev-devel libdrm-devel \
-            libinput-devel libxkbcommon-devel pixman-devel expat-devel libxml2-devel \
-            libffi-devel wayland-protocols xcb-util-errors-devel xcb-util-wm-devel \
-            xcb-util-renderutil-devel libxcb-devel xcb-util-cursor-devel xcb-util-devel \
-            xcb-util-image-devel xcb-util-keysyms-devel xcb-util-xrm-devel \
-            xorg-server-xwayland pkg-config meson git gcc pkgconf scdoc wget tar xz \
-            libevdev-devel
-
-          git clone https://gitlab.freedesktop.org/wayland/wayland.git
-          cd wayland
-          git checkout 1.20.0
-          meson build -Ddocumentation=false -Dtests=false --prefix /usr
-          ninja -C build install
-          cd ..
-
-          git clone https://gitlab.freedesktop.org/wlroots/wlroots.git
-          cd wlroots
-          git checkout 0.15.1
-          meson build --auto-features=enabled -Drenderers=gles2 -Dexamples=false \
-            -Dwerror=false -Db_ndebug=false --prefix /usr
-          ninja -C build install
-
-          wget -nv https://ziglang.org/download/0.9.1/zig-linux-x86_64-0.9.1.tar.xz
-          tar -xvf zig-linux-x86_64-0.9.1.tar.xz
-          mv zig-linux-x86_64-0.9.1/zig /usr/bin/
-          mv zig-linux-x86_64-0.9.1/lib /usr/lib/zig
-          zig env
-
-      - name: checkout
-        uses: actions/checkout@v2
-        with:
-          submodules: true
-
-      - name: build
-        run: |
-          zig build
-
-      - name: test
-        run: |
-          zig build test
-
-      - name: xwayland build
-        run: |
-          zig build -Dxwayland
-
-      - name: xwayland test
-        run: |
-          zig build -Dxwayland test
-
-      - name: fmt
-        run: |
-          zig fmt --check river/
-          zig fmt --check riverctl/
-          zig fmt --check rivertile/
-          zig fmt --check build.zig