freebsd-update: Do not fsync

Fsyncing each file we install slows us down significantly and adds
little to no safety.

MFC after:	1 week
PR:		287897

Author: dag-erling

usr.sbin/freebsd-update/freebsd-update.sh

@@ -3000,7 +3000,7 @@ install_from_index () {
 			if [ -z "${LINK}" ]; then
 				# Create a file, without setting flags.
 				gunzip < files/${HASH}.gz > ${HASH}
-				install -S -o ${OWNER} -g ${GROUP}	\
+				install -o ${OWNER} -g ${GROUP}		\
 				    -m ${PERM} ${HASH} ${BASEDIR}/${FPATH}
 				rm ${HASH}
 			else