Remove deprecated registration APIs (NFC)

In D104421, we changed the API for pass registration.
Before you would write:

      void registerPass("my-pass", "My Pass Description.",
                        [] { return createMyPass(); });
while now you’d only write:

      void registerPass([] { return createMyPass(); });

If you’re using TableGen to define your pass registration, you shouldn’t have anything to do. If you’re using directly the C++ API here are some changes.
Your project may also be broken even if you use TableGen and you call the
generated registration API in case your pass implementation didn’t inherit from
the MyPassBase class generated by TableGen.

If you don't use TableGen, the "my-pass" and "My Pass Description." fields must
be provided by overriding methods on the pass itself:

  llvm::StringRef getArgument() const final { return "my-pass"; }
  llvm::StringRef getDescription() const final {
    return "My Pass Description.";
  }

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D104429