Refactor: Move determinId to ubi

The function determinId is used only in ubi case, move it to ubi.

Tested: On the last commit of the patch series, run code update and
        factory reset on Witherspoon and all work fine.

Change-Id: I8974d25bf904a5202b913fc185790c5ecf8eca90
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/ubi/item_updater_ubi.cpp b/ubi/item_updater_ubi.cpp
index 1c2926a..354610b 100644
--- a/ubi/item_updater_ubi.cpp
+++ b/ubi/item_updater_ubi.cpp
@@ -487,7 +487,7 @@
     }
 }
 
-std::string ItemUpdater::determineId(const std::string& symlinkPath)
+std::string ItemUpdaterUbi::determineId(const std::string& symlinkPath)
 {
     if (!fs::exists(symlinkPath))
     {