kconfigini: Only open the file once to write
We were calling open(), then fopen(), then QFile::open(). This patch removes the fopen() call that does not seem to do anything.
Saw this while going through some code, figured I could just send it. Might be missing something otherwise obvious.
I'm also not sure why we open() then QFile::open(fd) instead of just opening, I guess it's related to the comment in the #else, so decided not to poke further.