docs: use UTF-8 instead of HTML entities for decorated letters

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>