Move the trademark entities from en_US.ISO8859-1/share/sgml to
share/sgml, since a lot of the entities are language independent, and
it makes work simpler for translators to have them in share/sgml.

The trademark.ent file contain:

• Commonly used trademarks defined as entities for ease of use.
• All trademark attributions defined as entities for ease of use.

Suggested by: hrs
Approved by: ceri (mentor)