Update vendored TPM simulator code to use TCG

The TPM reference code is now maintained by TCG at https://github.com/trustedcomputinggroup/tpm. We should update the vendored dependency to use that one.

If possible, we should consider using a git submodule for this to make the dependency easier to update. There may be reasons this isn't already the case, though.

Locate the vendored TPM reference code and inspect how this repository currently tracks and updates that dependency. Compare it with the TCG repository linked in the issue, then determine whether the dependency should be replaced directly or managed as a submodule; done means the repository uses the maintained TCG source and its update path is documented or established.

Written by the indexing model from the issue text.