[Session View] remove use of runtime mapping once endpoint fixes same_as_process boolean.

[mitodrummer]

Kibana version:
8.2

Describe the bug:
In order to query for all entry_session leaders for rendering in the sessions table, we currently need to use a complex runtime mapping. The ECS spec adds support for a entry_leader.same_as_process boolean, which can be used for this purpose.

e.g get all events WHERE process.entry_leader.same_as_process: true

Any additional context:
#127920 (comment)

[mitodrummer]

same_as_process should now be available in the latest endpoint-dev code.