No longer traverse files to get folder size.

Deleted DirectoryLoader and DirectoryLoaderTest. Added a method in
InspectorLoader for finding the number of items in a folder.

Refactored InspectorLoader to make it cleaner.

Bug: 63636562
Test: InspectorLoaderTest
Change-Id: Ib46e5f07917a87a67af0f6bab20dc8076e606c7b