This removes the use of the destructor in the move assignment operator, as it
may rely on undefined behaviour from the compiler. Additionally, some duplicate
logic to dereference and free a shared string has been unified under
_ReleasePrivateData().
Change-Id: Ie9f51d598c734f83cd0fba49b651315c6e9c8aac
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4440
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>