Remove libbfd dependency

[Philip Taylor]

To avoid problems like this, we should just remove the code that uses libbfd, since it's not particularly useful - it's just used for basic stack traces, which rarely provide enough useful information for debugging any problems, and we can easily get Linux users to run in gdb if we want more details.

[philip]

(In [8271]) Remove BFD-based debugging code, to avoid the runtime dependency on binutils. Fixes #581.