Removed platform specific reboot files for mellanox simx platforms (#10806)

- Why I did it
Platform_reboot files for simx doesn't do aything different apart from calling /sbin/reboot. which is anyway done in the /usr/local/bin/reboot script i.e. the parent script which calls the platform specific reboot scripts if present.

Moreover, /sbin/reboot invoked in the platform specific reboot script is a non-blocking call and thus it returns back to the original script (although /sbin/reboot does it job in the background) and we see messages like this.

Signed-off-by: Vivek Reddy Karri <[email protected]>

Author: vivekrnv