gh-37193: Some fixes & improvements to autogenerated flint .pxd
- flint autogen: fields of a[rc]b_poly_struct
- flint autogen: remove two typedefs that don't exist in flint
- move fix from #37064 to the flint interface generator
- flint autogen: add warnings about generated files to the templates
- regenerate flint wrappers
URL: https://github.com/sagemath/sage/pull/37193
Reported by: Marc Mezzarobba
Reviewer(s): Vincent Delecroix