Revert "[5.2] Load the namespace from the cached manifest"

[Fedik]

Reverts #44737

Reverting changes. For a few reasons:

• Loading a few bytes for nothing (in my test it add +100μs time to each request)
• The core does not read namespace from Db and we should not.

The PR for property deprecation #44754

If we need access to extension NS we need to plan a better API.
Currently I cannot sugest anything better, but having it like in the PR is not a good thing.

[laoneo]

Thanks!!