Removes the selected item from modules and module item move dialogs

fixes CNVS-15186

Test Plan:
  - Go to the modules page (/courses/##/modules)
  - Use the Move To... option in the settings cog menu to move
    a module.
  - In the dialog the module you selected to do this with should not
    be an option.
  - Repeat the same with a module item.
  - If you attempt to move the item within the save module, the item
    should not be displayed as an option.

Change-Id: If2649406570ae11fba0bca5b4910ed8fbcc6d84b
Reviewed-on: https://gerrit.instructure.com/40362
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>