Do not treat `isDefaultExpireDateEnforced` as fallback

Do not treat `isDefaultExpireDateEnforced` as fallback

`isDefaultExpireDateEnforced` and its corresponding `defaultExpirationDate`
is currently treated as the enforcement fallback when share type enforcements are not
set.

However, `isDefaultExpireDateEnforced` and `defaultExpirationDate` are actually more like
`isDefaultPublicExpireDateEnforced` and `defaultPublicExpirationDate` and therefore only applies
to public shares.

It might be ideal to rename this variables all the way from the backend config to the way we use
them in the frontend code.

Signed-off-by: fenn-cs <fenn25.fn@gmail.com>
Signed-off-by: nextcloud-command <nextcloud-command@users.noreply.github.com>