[debugger] Use BuildID field to get minidump build IDs

This is the end of the truncation madness. We're no longer stuffing GNU
build IDs into a Microsoft UUID field. We get the whole, correct build
ID every time. (Unless your crash came from a release before today, in
which case we're now pretending you don't exist).

Change-Id: I89567f399ff32db933350be8705ec0d79fa71619