adb shell
su
mount -o rw,remount /system
rm -rf /system/app/myApp.apk
rm -rf /data/data/com.example.myapp
mount -o ro,remount /system
exit
exit

Maybe this works:

adb shell rm /system/app/MyApp*
adb uninstall org.my.app

adb devices | tail -n 2 | head -n 1 | awk '{print $1}'