Remove language type from security training provider resolver and finder

We introduced language parameter in security training finders and GraphQL resolver in this issue. But later we decided to pass the filename instead of language type as part of #362697 (closed) which is merged in 15.1. As we are taking filename from where we will derive the language in backend, we can get rid of language parameter.

We are not going in the route to GraphQL deprecation as this parameter is introduced in 15.0(expired) and not used/consumed anywhere else (which was built for frontend in the first place).

Related to #364033 (closed)