Disable ed25519-donna's batch verification.

Fixes bug 40078.

As reported by hdevalence our batch verification logic can cause an assert
crash.

The assert happens because when the batch verification of ed25519-donna fails,
the code in `ed25519_checksig_batch()` falls back to doing a single
verification for each signature.

The crash occurs because batch verification failed, but then all signatures
individually verified just fine.

That's because batch verification and single verification use a different
equation which means that there are sigs that can pass single verification
but fail batch verification.

Fixing this would require modding ed25519-donna which is not in scope for
this ticket, and will be soon deprecated in favor of arti and
ed25519-dalek, so my branch instead removes batch verification.
9 jobs for bug40078 in 21 minutes and 10 seconds (queued for 14 minutes and 2 seconds)
latest
Status Name Job ID Coverage
  Test
passed debian-disable-dirauth #30559

00:10:11

passed debian-disable-relay #30560

00:09:55

passed debian-distcheck #30555

00:13:23

passed debian-docs #30556

00:06:09

passed debian-hardened #30554

00:13:21

passed debian-integration #30557

00:15:10

passed debian-minimal #30553

00:10:28

passed debian-nss #30561

00:09:03

passed debian-tracing #30558

00:12:29