Redundant error information

[GuillaumeGomez]

For the following code:

struct Bar;
struct Bar;

fn main () {
}

We get the following output:

error[E0428]: a type named `Bar` has already been defined in this module
  --> src/test/compile-fail/E0428.rs:12:1
   |
11 | struct Bar;
   | ----------- previous definition of `Bar` here
12 | struct Bar;
   | ^^^^^^^^^^^

error[E0428]: a value named `Bar` has already been defined in this module
  --> src/test/compile-fail/E0428.rs:12:1
   |
11 | struct Bar;
   | ----------- previous definition of `Bar` here
12 | struct Bar;
   | ^^^^^^^^^^^

error: aborting due to 2 previous errors

This is redundant, only one of the two would be enough.

cc @jonathandturner