date: Fix a few nits.

• Don't use asprintf() when strdup() can do the job just as well.
• Fix a couple of typos in a comment.

Fixes: eeb04a736cb9
MFC after: 3 days
Sponsored by: Klara, Inc.
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D46533

(cherry picked from commit a8ddd1926a34fc20970d9ceaad71b31fc414b1c5)

date: Documentation nits.

• Fix spurious capitalization.
• Fix inconsistent quoting.
• Use Dq rather than ASCII double quotes.

MFC after: 3 days
Sponsored by: Klara, Inc.
Reviewed by: 0mp
Differential Revision: https://reviews.freebsd.org/D46622

(cherry picked from commit 355ebf80b1ed98cf7ca9c51ce7e3e6dcb376853d)