Search for static method w/o overloads should be exact match in static import

Consider the following:
```groovy
import static Pogo.meth
class Pogo {
  static meth() {}
}
meth()
```

Searching for references (Ctrl+Shift+G) produces 1 exact match (the call `meth()`) and 1 potential match (in the static import).  Since there are no overloads, the reference is not ambiguous and should be indicated as exact.