proxy: go: don't free plugin twice

`proxy_go_input_init` no longer frees memory that is also cleaned up
on flb exit (e.g., a return from `flb_input_thread.c:flb_input_thread_instance_init:610`
sees a double free before this change).

Signed-off-by: Bradley Laney <[email protected]>

Author: stoksc

src/proxy/go/go.c

@@ -224,7 +224,6 @@ int proxy_go_input_init(struct flb_plugin_proxy *proxy)
     if (ret <= 0) {
         flb_error("[go proxy]: plugin '%s' failed to initialize",
                   plugin->name);
-        flb_free(plugin);
         return -1;
     }