Remove workaround for flushing wl_release events

This workaround was required when using Weston 3.0.91 or earlier
versions.

Change-Id: Ie89afb8644aaac156fd35a15b4bb8959065a9393
Signed-off-by: Fufu Fang <fufu.fang@arm.com>
1 job for features_wayland in 1 minute and 17 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #9338522
build_vulkan_wsi_layer

00:01:17