Temporary workaround for long failure messages when running from AS

AS installs tests in such a way that they don't get necessary
permissions; the result is a long message starting with "Failed to get
system health diags" when a test fails.

While I'm looking for a good solution, removing this annoyance.

Change-Id: I9e439c3aefb9dd365c841c98d530b9346d7ccd10
diff --git a/tests/tapl/com/android/launcher3/tapl/TestHelpers.java b/tests/tapl/com/android/launcher3/tapl/TestHelpers.java
index e882171..b8791e8 100644
--- a/tests/tapl/com/android/launcher3/tapl/TestHelpers.java
+++ b/tests/tapl/com/android/launcher3/tapl/TestHelpers.java
@@ -151,8 +151,7 @@
                     ? "Current time: " + new Date(System.currentTimeMillis()) + "\n" + errors
                     : null;
         } catch (Exception e) {
-            return "Failed to get system health diags, maybe build your test via .bp instead of "
-                    + ".mk? " + android.util.Log.getStackTraceString(e);
+            return null;
         }
     }
 }