Set `avb_keys=no_such_key` for dynamic kernel partitions to allow booting
unlocked devices with a custom kernel. This allows a few things:
1) Dogfooders can flash a custom kernel without wiping their device.
This can help developers track down hard-to-reproduce bugs without
rolling out a patch to the whole dogfooder population.
2) Developers can uprev their device's kernel without wiping their
device or packaging the kernel with an Android platform build.
Note: we are using "no_such_key" to ensure an AVB keys file doesn't
accidentally get created.
Test: Flash CI build. Then flash custom kernel on top.
Bug: 274825778
Change-Id: Ibf3cee491404b9efc18c49936edf64c2e3084adf
1bc7e21a38