An associated function for a trait was defined to be static, but an
implementation of the trait declared the same function to be a method (i.e., to
take a `self` parameter).
Erroneous code example:
```compile_fail,E0185
trait Foo {
fn foo();
}
struct Bar;
impl Foo for Bar {
// error, method `foo` has a `&self` declaration in the impl, but not in
// the trait
fn foo(&self) {}
}
```
When a type implements a trait's associated function, it has to use the same
signature. So in this case, since `Foo::foo` does not take any argument and
does not return anything, its implementation on `Bar` should be the same:
```
trait Foo {
fn foo();
}
struct Bar;
impl Foo for Bar {
fn foo() {} // ok!
}
```