Exported `integral` is in conflict

[mmikhasenko]

I've noticed that integral is exported since NumericalDistributions also exports integral and they are in conflict.

It would be good to find Julia standard integral interface and stick to it.
@Moelf do you know of any?

• I know of Polynomials that exports integrate.

[Moelf]

I don't know of any, happy to merge or remove, but remove will be a breaking change