Fixed issue with reseting logs

Summary:
Noticed that subsequent `adb logcat` invocations are stateful, and we didn't clear it's state when clearing the logs in memory.

This is a bandaid to get back to the previous behavior. I am wondering whether it wouldn't be just much more intuitive to always clear the logs (`adb logcat -c`) before we start the streaming log listener, so that users are never shown old logs from before flipper was connected?

Also fixed a leak in cleaning up the log listeners that was revealed by the possibility to disable the log plugin

Reviewed By: nikoant

Differential Revision: D26450262

fbshipit-source-id: 5b426e2d0e1fafdbc512d48d22b7bd4f30b61309

desktop/plugins/logs/index.tsx

@@ -497,6 +497,8 @@ export function devicePlugin(client: DevicePluginClient) {
   }
 
   function clearLogs() {
+    // Non public Android specific api
+    (client.device.realDevice as any)?.clearLogs?.();
     entries.set([]);
     rows.set([]);
     highlightedRows.set(new Set());