Remove libsurfaceflinger_unittest from root TEST_MAPPING

libsurfaceflinger_unittest has some flaky tests, and being run for all
frameworks/native changes means submitters are having to rerun
presubmit.

Bug: 186417847
Test: None (presubmit only)

Change-Id: I99f9fdf5e75dae686f958e97e9685d1a00166877
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 307e21c..4b64203 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -60,9 +60,6 @@
       ]
     },
     {
-      "name": "libsurfaceflinger_unittest"
-    },
-    {
       "name": "CtsGraphicsTestCases",
       "options": [
         {