docs: use UTF-8 instead of HTML entities for decorated letters
    
    We have files which use HTML entities for decorating letters
    with unlauts, accents, etc. Other files just use UTF-8
    characters directly for this. Remove the HTML entities since
    they have no benefit and use UTF-8 instead.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>