Unsize rules issues

[compiler-errors]

specification/src/types-and-traits.rst

Lines 2011 to 2012 in 496ef38

	* :dp:`fls_7aw3ifbvfgbd`
	``T`` implements ``core::marker::Unsize<U>``,

This rule is not required. This code compiles even though i32: Unsize<u32> is not true.

specification/src/types-and-traits.rst

Lines 2017 to 2020 in 496ef38

	* :dp:`fls_4wbk7pqj010i`
	The :t:`type` of ``last_field`` involves ``T`` and if the :t:`type` of
	``last_field`` is ``W<T>``, then ``W<T>`` implements
	``core::marker::Unsize<W<U>>``,

This rule should be generalized to allow multiple parameters to be changed. See the example committed in rust-lang/rust#117495 (tests/ui/unsized/unsize-coerce-multiple-adt-params.rs).

Also, this X field isn't referenced later in the document.