Revert "Bluetooth: Handle sub system restart gracefully"

This reverts commit b4bcafcb5327c5b4bcf89da60f09f6a063b034cc.
Our vendor implementations (broadcom, qcom, and ti) don't
have the cleanup method in bt_vendor_interface_t. Either patch
them all, or bt_vnd_if->ssr_cleanup() is going to break things

Change-Id: I1b90db7fd638783a97b25caeda6c0911dd26cfa5