Remove ScriptHostConfiguration object

[`ScriptHostConfiguration`](https://github.com/Azure/azure-webjobs-sdk-script/blob/dev/src/WebJobs.Script/Config/ScriptHostConfiguration.cs) is a mutable object that is created in few different places then shared across a bunch of other objects that all mutate it or recreate it. It's not possible to reason about the code at any place regarding what mysteries that instance might contain.