DOC: architecture: remove the totally outdated architecture manual

DOC: architecture: remove the totally outdated architecture manual

We've discussed about removing it many times and I thought it had been
removed long ago, but apparently not as William proved me. Let's get
rid of it now. It's totally outdated (last updated 18 years ago, when
laptop processors were still 32 bits), mentions keywords and external
products that don't exist anymore. It's not even on docs.haproxy.org.
At some point, old stuff must really die.