filesystem: fix run-answers for deleting a partition

When trying to delete a partition using the answers-based mechanism,
subiquity tries to call .done() on the ConfirmDeletesStretchy overlay.
However, this method does not exist. The .confirm() method is what we
should use instead.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/client/controllers/filesystem.py

@@ -216,7 +216,7 @@ class FilesystemController(SubiquityTuiController, FilesystemManipulator):
                 return
             if isinstance(body.stretchy, ConfirmDeleteStretchy):
                 if action.get("submit", True):
-                    body.stretchy.done()
+                    body.stretchy.confirm()
             else:
                 async for _ in self._enter_form_data(
                     body.stretchy.form, action["data"], action.get("submit", True)