Remove double & in KTabWidget

[Albert Astals Cid]

As you can see in ktabwidgettest after r939151 we are adding double && to it 
that causes accelerators not to work.

The culprit line is
  title.replace( '&', "&&" );
in
  KTabWidget::Private::updateTab

Removing it, the test (and kturtle that is what pointed me) work.

Tobias, blame says that line is yours, do you remember why you added it?

Ok, to remove it?

Albert