fix: remove bogus task which does nothing

The command doesn't change anything on the system, and the registered
variable `disk_usage` is never being used, moreover it gets overwritten
by the next task.

ansible/maintenance/maint-diskspace.yaml

@@ -3,10 +3,6 @@
   hosts: "{{ my_hosts | d([]) }}"
 
   tasks:
-    - name: Get disk usage
-      ansible.builtin.command: df -h
-      register: disk_usage
-
     - name: Check disk space available
       ansible.builtin.shell: df -Ph / | awk 'NR==2 {print $5}'
       register: disk_usage