general-functions: remove comment that system_output also in speed.cgi

this functions was removed from speed.cgi by reading kernel netowrk
statistics instead of parsing ip -s show ...

Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>

config/cfgroot/general-functions.pl

@@ -53,7 +53,6 @@ sub system_background($) {
 }
 
 # Returns the output of a shell command
-# if you change this also check speed.cgi that include a local copy for systemload reasons
 sub system_output($) {
 	my @command = @_;
 	my $pid;