oEmbed REST namespace has trailing slash

[rmccue]

The oEmbed namespace used when registering the routes has a trailing slash, which is redundant (and not recommended). This means that the namespace in the index doesn't match the expected format.

[swissspidy]

I assume changing it in the oEmbed controller is easier than in register_rest_route().

[rmccue]

Replying to swissspidy:

I assume changing it in the oEmbed controller is easier than in register_rest_route().

Indeed :) The route should continue to have the leading / though.

[rmccue]

In 35656:

oEmbed: Drop the trailing slash from the namespace.

Props swissspidy.
Fixes #34709.