Issue #18408: Don't check unicode consistency in _PyUnicode_HAS_UTF8_MEMORY()

and _PyUnicode_HAS_WSTR_MEMORY() macros

These macros are called in unicode_dealloc(), whereas the unicode object can be
"inconsistent" if the creation of the object failed.

For example, when unicode_subtype_new() fails on a memory allocation,
_PyUnicode_CheckConsistency() fails with an assertion error because data is
NULL.