Remove nonsensical body for trait getter
Remove nonsensical body for trait getter

This corrects an error in the change to the trait encoding
in #5003: getters in traits should have empty bodies and
be emitted as abstract.

```
% ~/scala/2.12.0-M4/bin/scalac sandbox/test.scala && javap -c T
Compiled from "test.scala"
public interface T {
  public abstract void T$_setter_$x_$eq(int);

  public int x();
    Code:
       0: aload_0
       1: invokeinterface #15,  1           // InterfaceMethod x:()I
       6: ireturn

  public int y();
    Code:
       0: aload_0
       1: invokeinterface #20,  1           // InterfaceMethod y:()I
       6: ireturn

  public void y_$eq(int);
    Code:
       0: aload_0
       1: iload_1
       2: invokeinterface #24,  2           // InterfaceMethod y_$eq:(I)V
       7: return

  public void $init$();
    Code:
       0: aload_0
       1: bipush        42
       3: invokeinterface #29,  2           // InterfaceMethod T$_setter_$x_$eq:(I)V
       8: aload_0
       9: bipush        24
      11: invokeinterface #24,  2           // InterfaceMethod y_$eq:(I)V
      16: return
}

% qscalac sandbox/test.scala && javap -c T
Compiled from "test.scala"
public interface T {
  public abstract void T$_setter_$x_$eq(int);

  public abstract int x();

  public abstract int y();

  public abstract void y_$eq(int);

  public static void $init$(T);
    Code:
       0: aload_0
       1: bipush        42
       3: invokeinterface #21,  2           // InterfaceMethod T$_setter_$x_$eq:(I)V
       8: aload_0
       9: bipush        24
      11: invokeinterface #23,  2           // InterfaceMethod y_$eq:(I)V
      16: return

  public void $init$();
    Code:
       0: aload_0
       1: invokestatic  #27                 // Method $init$:(LT;)V
       4: return
}
```

felixmulder/scala,slothspot/scala,jvican/scala,scala/scala,martijnhoekstra/scala,martijnhoekstra/scala,jvican/scala,shimib/scala,slothspot/scala,martijnhoekstra/scala,martijnhoekstra/scala,jvican/scala,lrytz/scala,shimib/scala,scala/scala,scala/scala,jvican/scala,jvican/scala,slothspot/scala,lrytz/scala,martijnhoekstra/scala,slothspot/scala,felixmulder/scala,scala/scala,lrytz/scala,jvican/scala,felixmulder/scala,felixmulder/scala,felixmulder/scala,shimib/scala,slothspot/scala,lrytz/scala,slothspot/scala,scala/scala,scala/scala,lrytz/scala,lrytz/scala,shimib/scala,slothspot/scala,felixmulder/scala,martijnhoekstra/scala,shimib/scala,shimib/scala,felixmulder/scala,jvican/scala