Remove unused private function importlib._bootstrap._object_name

[gaborbernat]

importlib._bootstrap._object_name(obj) has no caller and can be removed.

• gh-70319: Deprecate usage of load_module() #23469 (bpo-26131) added it to render an object's qualified name inside the load_module() deprecation warnings.
• Meta issue for cleaning up import system cruft #97850 (GH-97850: Remove all uses and definitions of load_module() from importlib #142205) removed load_module() and those warnings, deleting the last call site.

A word-boundary search across Lib, Modules, Python, Objects, and Include finds no reference outside its own definition, and a GitHub code search finds no downstream importer. The module is frozen, so removal also needs make regen-frozen.

Linked PRs

• gh-150886: Remove unused importlib._bootstrap._object_name #150884