Prevent double buffering from being disabled on USE_BE_CAIRO builds

Prevent double buffering from being disabled on USE_BE_CAIRO builds

The direct rendering code used in that situation never
completely worked, and the BDirectWindow destructor is also
buggy.  Completely remove that code in order to let us inherit
from BWindow, so as to prevent the buggy destructor from being
run.

* src/haiku_support.cc (cairo_format_from_color_space): Delete
function.
(class EmacsWindow): Inherit from BWindow.
(EmacsWindow): Call BWindow constructor instead.
(MessageReceived):
(DispatchMessage):
(FrameResized):
(FrameMoved):
(Zoom): Call BWindow functions instead.
(EmacsView_cairo_surface): Stop looking for surfaces in the
window.
(EmacsWindow_begin_cr_critical_section):
(EmacsWindow_end_cr_critical_section): Stop locking the window.

* src/haikufns.c (haiku_set_inhibit_double_buffering): Always
enable double buffering on Cairo builds.