Remove SecurityManager reference from API implementation

[scottkurz]

With the removal of the platform requirement to use SecurityManager, we can remove this from the API.

Note that:

• There is no mention of SecurityManager in the Jakarta Batch Specification
• There is no exposure of SecurityManager in any of the Jakarta Batch APIs, including jakarta.batch.runtime.BatchRuntime.

Because of this, the presence of SecurityManager in the BatchRuntime API implemented here is purely an implementation detail of the API code produced by the spec project. It is not an essential, specified part of the API, and so the specification does not need to be updated to remove it.

This can be removed in the next release then.

For reference here's the similar issue in the Jakarta REST project.