Duplicate assertion for presence of TDs

[egekorkan]

The two following assertions mean the same thing, one should be removed

• arch-td-mandatory: To be considered a Thing, however, at least one TD representation MUST be available.
• arch-td-metadata: In W3C WoT, the description metadata for a Thing instance MUST be available as a WoT Thing Description (TD)

[mlagally]

We can remove that as part of the PR transition depending on the results of the implementation report.

[mlagally]

Arch call on Nov 30th: This is not fatal, at this point we should not remove assertions, defer to next version of the architecture spec. If we need to do it earlier, we had to reopen the CR.