Bug 1548924 - task efficiency: remove sleep 15 clause from test-linux…

….sh r=gbrown,jmaher CLOSED TREE

Changes:
- remove the `sleep 15` clause.

Differential Revision: https://phabricator.services.mozilla.com/D30251

--HG--
extra : source : 0e9e744accd3ed7b7b0ff2436904ed78a92bf9e2

taskcluster/scripts/tester/test-linux.sh

@@ -134,9 +134,6 @@ if $NEED_WINDOW_MANAGER; then
     # This is read by xsession to select the window manager
     echo DESKTOP_SESSION=ubuntu > $HOME/.xsessionrc
 
-    # note that doing anything with this display before running Xsession will cause sadness (like,
-    # crashes in compiz). Make sure that X has enough time to start
-    sleep 15
     # DISPLAY has already been set above
     # XXX: it would be ideal to add a semaphore logic to make sure that the
     # window manager is ready