Move systemd to a separate snap part

snap/snapcraft.yaml

@@ -130,7 +130,6 @@ parts:
       - libxcb-screensaver0
       - zlib1g
       - glib-networking
-      - systemd
     cmake-generator: Ninja
     cmake-parameters:
       - -DCMAKE_BUILD_TYPE=Release
@@ -159,8 +158,6 @@ parts:
       rm -rf "$CRAFT_PART_INSTALL/usr/share/icons"
     stage:
       - -./usr/lib/$CRAFT_ARCH_TRIPLET/libjpeg.so.8.2.2
-    prime:
-      - -./lib/systemd
     after:
       - ffmpeg
       - libjxl
@@ -531,6 +528,13 @@ parts:
       - -./usr/lib/$CRAFT_ARCH_TRIPLET/*.so
       - -./usr/share
 
+  systemd:
+    plugin: nil
+    stage-packages:
+      - systemd
+    stage:
+      - ./usr/bin/systemd-detect-virt
+
   webrtc:
     source: https://github.com/desktop-app/tg_owt.git
     source-depth: 1