Don't use "interface" keyword unless really needed. The interface keyword
is defined as a preprocessor macro:

    #define interface struct

This was done by MS in order to be able to write this (which adds more
semantic):

 interface {
     HRESULT foo() = 0;
     [...]
 }

Change-Id: I95c6396158971220299cdc0ded6ffb11c677990c
Reviewed-by: Paolo Angelelli <paolo.angelelli@qt.io>