Remove useless comment.

It was misplaced (the line the comment was reffereing to has moved but
the comment hasn't) and it didn't explain anything that the actual line
didn't.

hosts/all.yaml

@@ -19,7 +19,6 @@ all:
       ansible_become: false
       ansible_connection: local
   vars:
-    # Force usage of Python3.
     ansible_become: true
     ansible_become_user: root
     ansible_connection: ssh