Revert "Ensure we produce a valid JSON while emptying the file"

This reverts commit 47e82a6343.

Podman wants an actual structure in the JSON file.

Change-Id: Ie5ecb3b074af479d7832fbab6611480175877956

tripleo_ansible/roles/tripleo-podman/tasks/tripleo_podman_install.yml

@@ -43,7 +43,7 @@
     - name: Remove default cni config for cni0 if exists
       copy:
         dest: /etc/cni/net.d/87-podman-bridge.conflist
-        content: '{}'
+        content: ''
         force: true
       when:
         - podman_bridge_config.stat.exists | bool