TAGS: reformat to fix when PRINTF_FMT() used.

I was wondering why TAGS was missing some functions, and finally
tracked it down: PRINTF_FMT() confuses etags if it's at the start
of a function, and it ignores the rest of the file.

So we put PRINTF_FMT at the end, but that doesn't work for
*definitions*, only *declarations*.  So we remove it from definitions
and add gratuitous declarations in the few static places.1

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/plugin.c

@@ -135,7 +135,7 @@ bool plugin_remove(struct plugins *plugins, const char *name)
 	return removed;
 }
 
-void PRINTF_FMT(2,3) plugin_kill(struct plugin *plugin, char *fmt, ...)
+void plugin_kill(struct plugin *plugin, char *fmt, ...)
 {
 	char *msg;
 	va_list ap;