Stop popping up the compatibility mode dialog all the time.

(The check for whether the dialog had already been shown was
accidentally removed in change I1c1bd12.)

Bug: 5069310
Change-Id: I2ea35c5891667922e78d7919132ffe599411f851
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java b/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java
index ae19cb1..7f56d45 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/tablet/TabletStatusBar.java
@@ -1077,7 +1077,10 @@
 
         mCompatModeButton.refresh();
         if (mCompatModeButton.getVisibility() == View.VISIBLE) {
+            if (DEBUG_COMPAT_HELP
+                    || ! Prefs.read(mContext).getBoolean(Prefs.SHOWN_COMPAT_MODE_HELP, false)) {
                 showCompatibilityHelp();
+            }
         } else {
             hideCompatibilityHelp();
             mCompatModePanel.closePanel();