admin::sudo: remove comment support

This is sparsely used and when it is, it's really obvious comments, so
this probably encourages a bad behavior. Besides, if there's something
really important that belongs into a comment, it can be placed in a
puppet comment; reading /etc/sudoers.d files manually isn't going to
give the full picture anyway.

Change-Id: I15506c376c811ce79ec1dfd6f0d714814e0dd670
Replace admin::sudo calls with sudo::user/group

admin::sudo was never meant for system users and it was misused across
the tree. Replace with sudo::user & sudo::group instead. The distinction
is subtle and is about to go away as part of a broader admin/sudo
consolidation.

Change-Id: I51ccfe7a5e1d8e1c341e5c0ece4385c62aafceca