Remove unused debug flag

Change-Id: I88ef517a5b4860c30f1eb2a52f15d8f07c823797
diff --git a/src/com/android/email/Email.java b/src/com/android/email/Email.java
index b9efaf4..24e64d7 100644
--- a/src/com/android/email/Email.java
+++ b/src/com/android/email/Email.java
@@ -71,11 +71,6 @@
     public static final boolean LOGD = false;
 
     /**
-     * If true, enable the UI thread check when accessing the filesystem.
-     */
-    public static final boolean DEBUG_THREAD_CHECK = false; // DON'T SUBMIT WITH TRUE
-
-    /**
      * If true, inhibit hardware graphics acceleration in UI (for a/b testing)
      */
     public static boolean sDebugInhibitGraphicsAcceleration = false;