crash: drop unused nanosecond precision

Currently we keep nanoseconds but do not use them and as a result we have
unneeded scaling. Let's use second precision which is on par with our
need.

Also drop ns_to_localtime. It can be written much shorter and it feels like
we don't need distinct function here. Like when we formatting time in
say.c.

NO_TEST=refactoring
NO_DOC=refactoring
NO_CHANGELOG=refactoring

(cherry picked from commit c457275a)