Fix google backup/restore functionality

This patch just reverts
Revert "Harden against transiently unavailable backup transports"
This reverts commit 28b6d3829166935f50684c0152a154cd4f1bbb90.

Revert "Handle backup transport registration dynamically"
This reverts commit c46c4a6765196bcabf3ea89771a1f9067b22baad.