json: do not escape single quotes

ECMA-404 standard does not include single quote character among the json
escape sequences. This means single quotes does not need to be escaped.

Indeed the single quote escape produces an invalid json output:

$ ip link add "john's" type dummy
$ ip link show "john's"
9: john's: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether c6:8e:53:f6:a3:4b brd ff:ff:ff:ff:ff:ff
$ ip -j link | jq .
parse error: Invalid escape at line 1, column 765

This can be fixed removing the single quote escape in jsonw_puts.
With this patch in place:

$ ip -j link | jq .[].ifname
"lo"
"john's"

Fixes: fcc16c2287 ("provide common json output formatter")
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>

lib/json_writer.c

@@ -80,9 +80,6 @@ static void jsonw_puts(json_writer_t *self, const char *str)
 		case '"':
 			fputs("\\\"", self->out);
 			break;
-		case '\'':
-			fputs("\\\'", self->out);
-			break;
 		default:
 			putc(*str, self->out);
 		}