gh-106320: Remove private _PyDict C API (#107145) Move private _PyDict functions to the internal C API (pycore_dict.h): * _PyDict_Contains_KnownHash() * _PyDict_DebugMallocStats() * _PyDict_DelItemIf() * _PyDict_GetItemWithError() * _PyDict_HasOnlyStringKeys() * _PyDict_MaybeUntrack() * _PyDict_MergeEx() No longer export these functions.