Fix issue with references to elements defined in an interface file

[cristianoc]

Fixes #645

References to elements defined in an interface file are not working. E.g.

module M: {
  let aa: int
} = {
  let aa = 10
}

let bb = M.aa
let cc = bb
let dd = M.aa
//          ^ref

The observed issue is that the locations of the references are fine, but the location of the definition in the module type is reported as being a ghost location (line -1).

This PR simply removes the ghost location from the results. Still need to look at why such ghost location is produced (go to definitions goes to the correct location in the module type).

For components, the JSX ppx produces 2 values called make shadowing one another, which triggers the compiler to generate a module constraint with a module type having only one make, and the same issue appears.