Remove hardcoded wrong summary

Change-Id: Ie96ec9387d77eccad404e3cc81bd0b48299f1c96
Fixes: 75260788
Test: reindexed search and manually search
diff --git a/res/xml/date_time_prefs.xml b/res/xml/date_time_prefs.xml
index 5219caa..bc11908 100644
--- a/res/xml/date_time_prefs.xml
+++ b/res/xml/date_time_prefs.xml
@@ -58,7 +58,7 @@
             android:fragment="com.android.settings.datetime.ZonePicker"
             android:key="timezone"
             android:title="@string/date_time_set_timezone"
-            android:summary="GMT-8:00"
+            android:summary="@string/summary_placeholder"
             settings:userRestriction="no_config_date_time" />
     </PreferenceCategory>