Function: remove_choice

--Usage--
> remove_choice(choice: some_strings, some_multiple_choice_value)

Deselect the given choice(s) from a [[type:value#multiple_choice|multiple choice value]],
returns the new value.

If a choice is not selected it is ignored.

--Parameters--
! Parameter	Type			Description
| @input@	[[type:string]]		Multiple choice value to look update.
| @choice@	[[type:string]]		Choice to remove.
| @choice1@	[[type:string]]		Remove multiple choices.
| @choice2@	[[type:string]]		''etc.''

--Examples--
> remove_choice(choice: "red",  "red")        ==  ""
> remove_choice(choice: "red",  "blue")       ==  "blue"
> remove_choice(choice: "red",  "red, blue")  ==  "blue"
> remove_choice(choice: "blue", "red, blue")  ==  "red"
> remove_choice(choice1: "red", choice2: "green", "red, blue")  ==  "blue"

--See also--
| [[fun:require_choice]]		Require that at least one of the given choices is selected.
| [[fun:exclusive_choice]]		Require that at most one of the given choices is selected.
| [[fun:require_exclusive_choice]]	Require that exactly one of the given choices is selected.