MFC r349286, r349293

Modify swapon(8) to invoke BIO_DELETE to trim swap devices, either if
'-E' appears on the swapon command line, or if "trimonce" appears as
an fstab option.

Remove #include <sys/types.h> to fix a style(9) violation.

Assisted by: alc
Release notes: yes
Approved by: kib (mentor)