Removes a ton of unused tablet vars, re-organizes the rest (#70344)

* Removes a ton of unused vars, re-organizes the rest

Removes a ton of unused vars from Modular computers
Re-organizes the rest, and adds autodoc comments to most of them
Moved 2 vars (saved_image and invisible) from the tablet to the messenger app, since that's where it was used. I didn't see the point of having these vars be on every computer anyways, only PDAs have the app.
Renames Clown's honk virus var
Makes Messenger app's saved image, actually used.

* static list and NODECONSTRUCT_1 check

* oops

code/modules/modular_computers/computers/machinery/modular_computer.dm

@@ -12,7 +12,7 @@
 
 	idle_power_usage = BASE_MACHINE_IDLE_CONSUMPTION * 0.05
 	///A flag that describes this device type
-	var/hardware_flag = 0
+	var/hardware_flag = NONE
 	///Power usage during last tick
 	var/last_power_usage = 0
 	/// Amount of programs that can be ran at once