UEFI signing failures cause binaries to be republished continuously

A UEFI signing failure (or possibly any CustomUploadError) during process-accepted causes the PackageUpload to remain ACCEPTED, even though BPPHs have already been created (and will be committed, as process-accepted deliberately commits even upon failure). The next run of process-accepted does the same thing, and the next, and the next, causing unbounded republication of the upload's binaries.

ppa:apw/signing has more than 120000 excess publications, and ppa:jacob/ppa has somewhere north of 343000 of them. There are more than likely other less bad cases.

We might just want to skip signing if there's no key, but that won't fix the ppa:apw/signing case, which is failing with this error:

 warning: file-aligned section .text extends beyond end of file
 warning: checksum areas are greater than image size. Invalid section table?