[SetUI] Remove backward-compatible build tag code

Bug ID: SU-246 #done
Tests: fx run-host-tests settings_tests

Change-Id: Ib327ac4f2386deb7b19d44a8b9be25a685d9e16e
diff --git a/lib/settings/lib/device_info.dart b/lib/settings/lib/device_info.dart
index 2c43c1f..013e32a 100644
--- a/lib/settings/lib/device_info.dart
+++ b/lib/settings/lib/device_info.dart
@@ -37,16 +37,6 @@
     return null;
   }
 
-  /// Backwards compatibility, TODO: remove later [SU-246]
-  static DateTime getSourceDate() {
-    try {
-      return DateTime.parse(sourceDate.trim());
-    } on FormatException {
-      log.warning('Could not parse build timestamp!');
-    }
-    return null;
-  }
-
   /// Sets a flag to determine whether the device should be reset to factory
   /// settings or not.
   ///