[3.10] bpo-46006: Revert "bpo-40521: Per-interpreter interned strings (GH-20085)" (GH-30422) by vstinner · Pull Request #30425

[3.10] bpo-46006: Revert "bpo-40521: Per-interpreter interned strings (GH-20085)" (GH-30422) by vstinner · Pull Request #30425 · python/cpython

)" (GH-30422)

This reverts commit ea25180.

Keep "assert(interned == NULL);" in _PyUnicode_Fini(), but only for
the main interpreter.

Keep _PyUnicode_ClearInterned() changes avoiding the creation of a
temporary Python list object.

(cherry picked from commit 35d6540)