rc-httpd: only emit charset option for text/plain content type

rc/bin/rc-httpd/handlers/serve-static

@@ -36,7 +36,7 @@ case *
 max_age=3600	# 1 hour
 echo 'HTTP/1.1 200 OK'^$cr
 emit_extra_headers
-echo 'Content-type: '^$type^'; charset=utf-8'^$cr
+echo 'Content-type: '^$type^$cr
 echo 'Content-length: '^`{ls -l $full_path | awk '{print $6}'}
 echo 'Cache-control: max-age='^$max_age^$cr
 echo $cr