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/app/src/sandy-chrome/appinspect/LaunchEmulator.tsx

@@ -76,7 +76,9 @@ export const LaunchEmulatorDialog = withTrackingScope(
     }, [iosEnabled, getSimulators, store]);
 
     const items = [
-      ...(androidEmulators.length > 0 ? [<AndroidOutlined />] : []),
+      ...(androidEmulators.length > 0
+        ? [<AndroidOutlined key="android logo" />]
+        : []),
       ...androidEmulators.map((name) => {
         const launch = (coldBoot: boolean) => {
           launchEmulator(name, coldBoot)
@@ -111,7 +113,7 @@ export const LaunchEmulatorDialog = withTrackingScope(
           </Dropdown.Button>
         );
       }),
-      ...(iosEmulators.length > 0 ? [<AppleOutlined />] : []),
+      ...(iosEmulators.length > 0 ? [<AppleOutlined key="ios logo" />] : []),
       ...iosEmulators.map((device) => (
         <Button
           key={device.udid}