gh-106320: Remove private _Py_UniversalNewlineFgetsWithSize() (#108602)

The remove private _Py_UniversalNewlineFgetsWithSize() function from
the public C API: move it the internal C API (pycore_fileutils.h).
No longer export the function.

Author: vstinner

Include/cpython/fileobject.h

@@ -3,7 +3,6 @@
 #endif
 
 PyAPI_FUNC(char *) Py_UniversalNewlineFgets(char *, int, FILE*, PyObject *);
-PyAPI_FUNC(char *) _Py_UniversalNewlineFgetsWithSize(char *, int, FILE*, PyObject *, size_t*);
 
 /* The std printer acts as a preliminary sys.stderr until the new io
    infrastructure is in place. */

Include/internal/pycore_fileutils.h

@@ -315,6 +315,8 @@ extern HRESULT PathCchSkipRoot(const wchar_t *pszPath, const wchar_t **ppszRootE
 // Export for 'select' shared extension (Argument Clinic code)
 PyAPI_FUNC(int) _PyLong_FileDescriptor_Converter(PyObject *, void *);
 
+extern char* _Py_UniversalNewlineFgetsWithSize(char *, int, FILE*, PyObject *, size_t*);
+
 #ifdef __cplusplus
 }
 #endif