Remove an unneeded 'tail -n 1' from a pipeline

When piping to awk, it's almost always an anti-pattern to use 'grep'
first.

When not in a pipeline, sometimes it is faster to use tail, as awk
must process all the lines in the input stream, and won't 'seek'.
In a pipeline, both grep and awk must process all lines, so we might
as well skip the extra process creation for tail and just use awk
for all the processing.

Reviewed by: jilles
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D19441