Remove RuntimeAPIDelegate::GetPreviousVersion.

extensions/shell/browser/shell_runtime_api_delegate.cc

Index: extensions/shell/browser/shell_runtime_api_delegate.cc
diff --git a/extensions/shell/browser/shell_runtime_api_delegate.cc b/extensions/shell/browser/shell_runtime_api_delegate.cc
index 1d0a06fa8bdab594d67d28ca806bb39962ee6872..ec04668efca1e360f640357bab7a908143b40e8d 100644
--- a/extensions/shell/browser/shell_runtime_api_delegate.cc
+++ b/extensions/shell/browser/shell_runtime_api_delegate.cc
@@ -28,11 +28,6 @@ void ShellRuntimeAPIDelegate::AddUpdateObserver(UpdateObserver* observer) {
 void ShellRuntimeAPIDelegate::RemoveUpdateObserver(UpdateObserver* observer) {
 }
 
-base::Version ShellRuntimeAPIDelegate::GetPreviousExtensionVersion(
-    const Extension* extension) {
-  return base::Version();
-}
-
 void ShellRuntimeAPIDelegate::ReloadExtension(const std::string& extension_id) {
 }