Fixing Duplicate interface definition errors when using via cocoapods

**Disclaimer**: I may be doing something very wrong. I apologize if that's the case :)

I was using `Mantle` as a submodule and just compiling the Mantle source along with my project and that worked just fine, that's why I think this may be something I'm doing wrong.

The `Pods` target fails to compile when I added the `Mantle` dependency because it complained that some classes were duplicated.

Removing those imports seems to fix this?