[examples] Rename LLJITWithJITLink to LLJITWithCustomObjectLinkingLayer.

LLJIT now uses JITLink/ObjectLinkingLayer by default where available, so
these steps aren't required to use it. The tutorial is still useful though:
Clients can use it to test altervative linking layer implementations (e.g.
handing off to the system linker) or to test implementations of JITLink that
are still under development.