Documentation: rust: Fix arch support table

Documentation: rust: Fix arch support table

Stephen Rothwell reported htmldocs warning when merging uml tree:

Documentation/rust/arch-support.rst:20: WARNING: Blank line required after table.

Fix the arch support table by removing extraneous simple table marker.

Link: https://lore.kernel.org/linux-next/20230213152714.78b844f4@canb.auug.org.au/
Fixes: 0438aadfa69a34 ("rust: arch/um: Add support for CONFIG_RUST under x86_64 UML")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>