Fix for issue 210

[jespercockx]

This fixes #210 by using the same way to track module parameters that should be dropped as Agda uses internally. It also removes support for functions inside record modules (as in the test case for #185) since these do not exist in Haskell in the first place.

[jespercockx]

@viktorcsimma WDYT?

[viktorcsimma]

It's exactly what I needed; thank you! I've tested it with my project and it works flawlessly.

I agree that if we have to choose between #210 and #185; #210 is more important. I used to depend on agda-stdlib where there sometimes are functions in record namespaces, but that's a quite rare use case.