common: remove json_stream_log_suppress

The function is tiny and was only used in one location. And that one
location was leaking memory.

Detected by ASan:

==2637667==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 7 byte(s) in 1 object(s) allocated from:
    #0 0x4cd758 in __interceptor_strdup
    #1 0x64c70c in json_stream_log_suppress_for_cmd lightning/lightningd/jsonrpc.c:597:31
    #2 0x68a630 in json_getlog lightning/lightningd/log.c:974:2
    ...

SUMMARY: AddressSanitizer: 7 byte(s) leaked in 1 allocation(s).

common/json_stream.c

@@ -95,13 +95,6 @@ static bool json_stream_still_writing(const struct json_stream *js)
 	return js->writer != NULL;
 }
 
-void json_stream_log_suppress(struct json_stream *js, const char *cmd_name)
-{
-	/* Really shouldn't be used for anything else */
-	assert(streq(cmd_name, "getlog"));
-	js->log = NULL;
-}
-
 void json_stream_append(struct json_stream *js,
 			const char *str, size_t len)
 {

common/json_stream.h

@@ -97,9 +97,6 @@ const char *json_stream_detach_filter(const tal_t *ctx, struct json_stream *js);
  */
 void json_stream_close(struct json_stream *js, struct command *writer);
 
-/* For low-level JSON stream access: */
-void json_stream_log_suppress(struct json_stream *js, const char *cmd_name);
-
 /* '"fieldname" : [ ' or '[ ' if fieldname is NULL */
 void json_array_start(struct json_stream *js, const char *fieldname);
 /* '"fieldname" : { ' or '{ ' if fieldname is NULL */

lightningd/jsonrpc.c

@@ -594,8 +594,10 @@ void json_stream_log_suppress_for_cmd(struct json_stream *js,
 	const char *nm = cmd->json_cmd->name;
 	const char *s = tal_fmt(tmpctx, "Suppressing logging of %s command", nm);
 	log_io(cmd->jcon->log, LOG_IO_OUT, NULL, s, NULL, 0);
-	json_stream_log_suppress(js, strdup(nm));
 
+	/* Really shouldn't be used for anything else */
+	assert(streq(nm, "getlog"));
+	js->log = NULL;
 }
 
 static struct json_stream *json_start(struct command *cmd)