Revert "Don't delete uploaded posts when refreshing. Also only set list post adapter if it doesn't exist yet, which fixes bug where scroll position would be lost when returning to the posts list from another activity."

This reverts commit cb27091bf2cd8a698cae306dc0cf72b950a83221.
Also only set list post adapter if it doesn't exist yet, which fixes bug where scroll position would be lost when returning to the posts list from another activity.