Python3 Cleanup

[Zelec]

To make it clear, I didn't do these edits, @andymcca did in the sshflash-win repo I'm just pushing some of the cleanup I did to make flashing RetroLeap work with python3 on my laptop.

No real code tweaks required, all worked fine on Linux with Python 3.11 to flash my LeapPad 2 (more testing with other hardware may be required)

Only four cleanup items done on my end that didn't already exist

• reverted .exe references back to .py
• Updated shebangs to reference /usr/bin/env across the board (most already had this)
• Updated python shebangs to target python3
• Updated remote_flash.sh to reference python3 instead of python2

[Zelec]

Forgot to include this is to close Issue #6