backport of: win64,stackwalk: remove support for binaries missing SEH info
This hack, added in 7e95d0911110e6d4fdfb5c9e96cd5957ad27d259, was a
workaround for LLVM3.3 not being able to generate binaries with the
mandatory SEH section information. Now, it is just a potential source of
segfaults in observation.