[PricingBundle] Remove unnecessary complexity

[aramalipoor]

@pjedrzejewski @stloyd I'm working on a AngularJS admin and now that I'm working on field prototypes this portion of code is breaking my code.

I expect prototypes var to contain an associative array in which the keys are exactly equal to the values that the "value provider" field generates (in this PricingBundle case, the pricingCalculator is the "value provider").

So that I can find appropriate calculator prototype based on current pricingCalculator value on my forms.

I took a quick look around the whole source code and couldn't find any use of $group prefix for prototypes array.

[stloyd]

@aramalipoor Sounds reasonable for me.

[pjedrzejewski]

Cool, thank you!