*: Do not use the no-op -r flag for bsdlabel(8)

The -r flag is ignored by the FreeBSD implementation of bsdlabel(8)
(also called disklabel(8) in the past). Remove its use from examples
and tests in the tree.

This commit does not touch historical documentation under share/doc/smm
and files under contrib/netbsd-tests.

Reviewed by: imp
MFC after: 2 weeks
Approved by: imp (src)
Fixes: 57dfbec57b6d More axe-work:
Differential Revision: https://reviews.freebsd.org/D34585