graphics_utils.xcommand: Remove X11 remants

Delete usage of graphics_utils.xcommand before delete it in graphics_utils.py

BUG=chromium:655820
TEST=test_that

Change-Id: Ia2af3cc811a23d6ce2c89a3e664be3a72f75c545
Reviewed-on: https://chromium-review.googlesource.com/493897
Commit-Ready: Po-Hsien Wang <pwang@chromium.org>
Tested-by: Po-Hsien Wang <pwang@chromium.org>
Tested-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
diff --git a/client/site_tests/camera_V4L2/camera_V4L2.py b/client/site_tests/camera_V4L2/camera_V4L2.py
index f1f745b..a7b66cb 100644
--- a/client/site_tests/camera_V4L2/camera_V4L2.py
+++ b/client/site_tests/camera_V4L2/camera_V4L2.py
@@ -144,6 +144,5 @@
 
         executable = os.path.join(self.bindir, "media_v4l2_test")
         cmd = "%s %s" % (executable, " ".join(options))
-        cmd = graphics_utils.xcommand(cmd)
         logging.info("Running %s" % cmd)
         stdout = utils.system_output(cmd, retain_output=True)
diff --git a/client/site_tests/graphics_Gbm/graphics_Gbm.py b/client/site_tests/graphics_Gbm/graphics_Gbm.py
index b97aba1..f12e5c3 100644
--- a/client/site_tests/graphics_Gbm/graphics_Gbm.py
+++ b/client/site_tests/graphics_Gbm/graphics_Gbm.py
@@ -31,7 +31,6 @@
 
     def run_once(self):
         cmd = os.path.join(self.srcdir, 'gbmtest')
-        cmd = graphics_utils.xcommand(cmd)
         result = utils.run(cmd,
                            stderr_is_expected=False,
                            stdout_tee=utils.TEE_TO_LOGS,
diff --git a/client/site_tests/graphics_SanAngeles/graphics_SanAngeles.py b/client/site_tests/graphics_SanAngeles/graphics_SanAngeles.py
index 9d340a5..3d2fad1 100644
--- a/client/site_tests/graphics_SanAngeles/graphics_SanAngeles.py
+++ b/client/site_tests/graphics_SanAngeles/graphics_SanAngeles.py
@@ -54,7 +54,6 @@
                 (cmd_gl, cmd_gles, cmd_gles_s))
 
         cmd += ' ' + utils.graphics_platform()
-        cmd = graphics_utils.xcommand(cmd)
         result = utils.run(cmd,
                            stderr_is_expected=False,
                            stdout_tee=utils.TEE_TO_LOGS,