Remove unnecessary evals that do-fetch was using.

Turns out that env(1) knows how to parse a properly quoted string
using -S "string", it makes the double eval used for the fetch
command to be unnecessary.

This is because running:
eval "foo $(escape $bar)"
is silly when this works:
foo $bar

So remove escaping and quoting, and sillyness.

PR: 210198
Submitted by: mat
Exp-run by: antoine
Sponsored by: The FreeBSD Foundation, Absolight
Differential Revision: https://reviews.freebsd.org/D6779