Remove support for building with system libraries

.github/workflows/ci.yml

@@ -4,7 +4,7 @@ name: Continuous integration
 
 jobs:
   ubuntu-build-bundled:
-    name: "Ubuntu: Build with bundled libraries"
+    name: Ubuntu
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -32,53 +32,8 @@ jobs:
       - name: Build
         run: cmake --build build
 
-  ubuntu-build-system:
-    name: "Ubuntu: Build with system libraries"
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - name: Checkout submodules
-        run: git submodule update --init
-      - name: Install dependencies
-        run: sudo apt-get update && sudo apt-get install -y
-          ffmpeg
-          libasound2-dev
-          libgl-dev
-          libglew-dev
-          libgtk-3-dev
-          libjack-dev
-          libjsoncpp-dev
-          libmad0-dev
-          libpng-dev
-          libpulse-dev
-          libtomcrypt-dev
-          libtommath-dev
-          libudev-dev
-          libva-dev
-          libvorbis-dev
-          libxinerama-dev
-          libx11-dev
-          libxrandr-dev
-          libxtst-dev
-          ninja-build
-      - name: Configure
-        run: cmake -G Ninja -B build
-          -DWITH_SYSTEM_FFMPEG=ON
-          -DWITH_SYSTEM_GLEW=ON
-          -DWITH_SYSTEM_JPEG=ON
-          -DWITH_SYSTEM_JSONCPP=ON
-          -DWITH_SYSTEM_MAD=ON
-          -DWITH_SYSTEM_OGG=ON
-          -DWITH_SYSTEM_PCRE=ON
-          -DWITH_SYSTEM_PNG=ON
-          -DWITH_SYSTEM_TOMCRYPT=ON
-          -DWITH_SYSTEM_TOMMATH=ON
-          -DWITH_SYSTEM_ZLIB=ON
-      - name: Build
-        run: cmake --build build
-
   macos-build-bundled:
-    name: "macOS: Build with bundled libraries"
+    name: macOS
     runs-on: macos-latest
     steps:
       - uses: actions/checkout@v2
@@ -93,7 +48,7 @@ jobs:
         run: cmake --build build
 
   windows-build-bundled:
-    name: "Windows: Build with bundled libraries"
+    name: Windows
     runs-on: windows-latest
     steps:
       - uses: actions/checkout@v2