endian.h: Remove duplicate words

Reviewed by: emaste
Pull Request: https://github.com/freebsd/freebsd-src/pull/920

(cherry picked from commit dff3a80f6dfe88c52326ceb2c154668f132fdb52)
(cherry picked from commit 4e1deb61eab2037ab53cebf7d5dd688626d6f094)