Don't generate stack in logcat if assistant missing.

Low ram devices don't have assistants. Worth noting, but not
making a big stink about it.

Change-Id: I5a49be99bf688a5f1b800a1124b14a589ecf5b52
Fixes: 27210719

packages/SystemUI/src/com/android/systemui/assist/AssistManager.java

@@ -247,8 +247,8 @@ public class AssistManager {
                     }
                 }
             } catch (PackageManager.NameNotFoundException e) {
-                Log.w(TAG, "Failed to swap drawable; "
-                        + component.flattenToShortString() + " not found", e);
+                Log.v(TAG, "Assistant component "
+                        + component.flattenToShortString() + " not found");
             } catch (Resources.NotFoundException nfe) {
                 Log.w(TAG, "Failed to swap drawable from "
                         + component.flattenToShortString(), nfe);