Unbinds ahelp due to it being doubled up (#4749)

# About the pull request

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This removes the default bind for AdminHelp because SSinput already has
an hardcoded bind for it, causing it to fire twice. You're still welcome
to also bind ahelp to another key. This does not affect existing users
because it only changes the default preset.

# Explain why it's good for the game
It's less of an issue with the new tgui ahelp box but has been a thing
forever and still doubles up the chat help message.

# Testing Photographs and Procedure
Reset keybinds, pressed F1, tried reloading game etc


# Changelog
:cl:
fix: Removed redundant double binding for F1 to AdminHelp from default
keybinds. This does not affect existing users or their settings.
/:cl:

code/datums/keybinding/client.dm

@@ -4,8 +4,8 @@
 
 
 /datum/keybinding/client/admin_help
-	hotkey_keys = list("F1")
-	classic_keys = list("F1")
+	hotkey_keys = list("Unbound")
+	classic_keys = list("Unbound")
 	name = "admin_help"
 	full_name = "Admin Help"
 	description = "Ask an admin for help."