glx: Don't enable INTEL_swap_event unconditionally

DRI2 supports this now - and already enables it explicitly - but drisw
does not and should not.  Otherwise toolkits like clutter will only ever
SwapBuffers once and wait forever for an event that's not coming.

Signed-off-by: Adam Jackson <ajax@redhat.com>

src/glx/glxextensions.c

@@ -139,7 +139,7 @@ static const struct extension_info known_glx_extensions[] = {
    { GLX(SGIX_visual_select_group),    VER(0,0), Y, Y, N, N },
    { GLX(EXT_texture_from_pixmap),     VER(0,0), Y, N, N, N },
 #endif
-   { GLX(INTEL_swap_event),            VER(1,4), Y, Y, N, N },
+   { GLX(INTEL_swap_event),            VER(1,4), Y, N, N, N },
    { NULL }
 };