window: Remove suspicious branch

window: Remove suspicious branch

While this commit was found to make emacs windows shrink (and it was
reverted in the gtk-3-20 branch for that reason), that was the only
observed breakage, while the reversal broke several of our unit tests.

Closer study of the emacs sources revealed that it does some really
unsupportable things like doing its own X event handling behind GTK+'s
back and freely mixing sizes of GtkWindows and GdkWindows obtained in
various ways. I've filed a bug against emacs with suggestions for how
to avoid the shrinking window, regardless of this commit.

Original commit message:

It seems this branch is not needed anymore. It was originally added in
1999 to support gtk_widget_realize(), but all those reasons seem
obsolete today.
Instead just call gtk_widget_realize().

If you end up at this commit when bisecting:
There is no bug that made me remove this code, it was purely meant to be
cleanup / dead code removal. I seem to have introduced a new bug or
bisecting wouldn't have let you here. So it seems we should just revert
this commit.