Delete unused bin directory

Delete last bits of bin/.  With the move to entrypoints these aren't
needed anymore.

Update CONF.bindir to default to
  os.path.join(sys.prefix, 'local', 'bin')

Part of blueprint entrypoints-plugins

Change-Id: I95250d3779433e7b85aaa889a873b16c86a7d2be
Merge "Delete unused bin directory"