krb5: Make the build a bit quieter

compile_et.sh is run during buildworld and prints a bunch of debug
output. It's intrusive and probably not needed, at least by default, so
let's make the build output a bit cleaner. This is an upstream script,
but it hasn't been modified in 15 years so the local modification is
unlikely to cause any pain.

Also remove a print that shows up in buildworld -s output.

Reviewed by: cy
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D55317

(cherry picked from commit 4c247f120492d999ac90efcfc73e5fea29206d1f)