swap_repository: Fix minor warnings reported by pylint

  W: 51,0: Unused import gmtime
  W: 51,0: Unused import strftime
  W:100,51:determine_dest_dir: Unused argument 'component_name'

Change-Id: I8d631e107ad4b5d818a508ce87c0a7b21193167d
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>