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

sys/kern/makesyscalls.sh

@@ -65,7 +65,6 @@ if [ -n "$2" ]; then
 fi
 
 sed -e '
-s/\$//g
 :join
 	/\\$/{a\
 
@@ -147,7 +146,7 @@ s/\$//g
 		printf " * $%s$\n", "FreeBSD" > systrace
 	}
 	NR == 1 {
-		gsub("[$]FreeBSD: ", "", $0)
+		gsub("[$]FreeBSD: ", "FreeBSD: ", $0)
 		gsub(" [$]", "", $0)
 
 		printf " * created from%s\n */\n\n", $0 > syssw