makesyscalls.sh: remove trailing space on the "created from" line

In r10905 and r10906 makesyscalls was modified to avoid emitting a
literal $Id$ string in the generated file, with:

gsub("[$]Id: ", "", $0)
gsub(" [$]", "", $0)

Then r11294 added some functionality and also tried to address the $Id$
problem in a different way, by removing every $:

sed -e 's/\$//g ...

This rendered the gsub infeffective. The gsub was later updated to
track the $Id$ -> $FreeBSD$ switch, even though it did not do anything.

Revert the addition of the s/\$//g, and update the gsub to keep the
resulting format the same.

Discussed with: bde
MFC after: 1 week
Sponsored by: The FreeBSD Foundation