Remove HubSpot.NET.Core.ReflectionExtensions

[Psypher9]

The ReflectionExtensions class does not have any references outside of it self. Since v1 will be changing the serialization strategy/methodology entirely, these might not be needed at all.

Thoughts?

[clarkd]

Seems to make sense to me - although might be worth holding off until we've figured out #37 and how we'll be supporting custom models going forwards, as that might use some of the reflection code?

[Psypher9]

Well, I tracked down all of the references and there currently aren't any and all of these extensions were previously used in the now deprecated RequestSerializer and RequestDataConverter.

[clarkd]

@Psypher9 I just meant that we might still need some of that code given that the custom models don't work properly right now? Happy to remove if it's still unused after we've figured that out!