I completely disagree to call it redundant. It would make Mednafen PSX version in RetroArch inferior to the original if anyone is thinking like this. Who is to say which peripheral is redundant and which not? There are some good games for lightgun that people played some years ago and would like to experience it again - and they are going to find lightguns are not supproted because someone thought of them as being redundant? People use it, then it is needed - just one example: http://forum.fobby.net/index.php?t=tree&th=978&start=0&
Anyway, you already support lightguns - justifiers. See - some developer not thought about them as being redundant 
In 1.0.0.2 version some of them are missing or some even are unknown like SuperScope - whatever that is. I think it is much better to just use same names (not like this SuperScope that probably means a lightgun), not choose which are redundant and which arent, because then there is a complete mess like even having “multitap” there or “justifier” and “justifiers” devices.
Here is a whole list from Mednafen documentation:
none - none
gamepad - Digital Gamepad
PlayStation digital gamepad; SCPH-1080.
dualshock - DualShock
DualShock gamepad; SCPH-1200. Emulation in Mednafen includes the analog mode toggle button. Rumble is emulated, but currently only supported on Linux, and MS Windows via the XInput API and XInput-compatible gamepads/joysticks. If you're having trouble getting rumble to work on Linux, see if Mednafen is printing out error messages during startup regarding /dev/input/event*, and resolve the issue(s) as necessary.
dualanalog - Dual Analog
Dual Analog gamepad; SCPH-1180. It is the predecessor/prototype to the more advanced DualShock. Emulated in Mednafen as forced to analog mode, and without rumble.
analogjoy - Analog Joystick
Flight-game-oriented dual-joystick controller; SCPH-1110. Emulated in Mednafen as forced to analog mode.
mouse - Mouse
negcon - neGcon
Namco's unconventional twisty racing-game-oriented gamepad; NPC-101.
guncon - GunCon
Namco's light gun; NPC-103.
justifier - Konami Justifier
Konami's light gun; SLUH-00017. Rumored to be wrought of the coagulated rage of all who tried to shoot The Dog. If the game you want to play supports the "GunCon", you should use that instead. NOTE: Currently does not work properly when on any of ports 1B-1D and 2B-2D.
dancepad - Dance Pad
Dingo Dingo Rodeo!