upstream fixes for default mame2003 keyboard mapping

[markwkidd]

I am posting to make sure that folks like @obsidianspider , @dankcushions, @Rion and others who help support MAME users are aware of my patch to mame2003 which was just merged: https://github.com/libretro/mame2003-libretro/pull/316

What did this fix?
Folks that use keyboards or devices that appear as keyboards (for me, the X-Arcade Tankstick to be specific) it has sometimes been problematic that there are conflicts between the RetroArch keybindings and the default MAME keybindings.

Also it is the case that there were some deprecated MAME functions and some redundant MAME functions that were bound to the keyboard. For example, MAME's internal pause was mapped to 'P', just as RA's pause. The result was erratic 'double-pausing.' Another example is that there were still bindings for the MAME native FPS display even though that functionality has been long removed from mame2003.

TL/DR
For most users, and probably even most MAME keyboard/Tankstick users, there should be no change after this PR is incorporated into their core. If someone has used the mame2003 TAB menu to remap these conflicting keys in the past, or perhaps for other less common use cases, this could cause people to post help requests.

I'll try to keep an eye out for any posts that seem to stem from this change to help many any adjustment pains minimal. There may not be any pains at all but I just wanted to spread the word a bit as a preventative measure! :)

[Rion]

@markwkidd Word received 😀. Great work as always 😎