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: 0438aadf ("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>

Documentation/rust/arch-support.rst

@@ -16,6 +16,6 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
 Architecture  Level of support  Constraints
 ============  ================  ==============================================
 ``x86``       Maintained        ``x86_64`` only.
-============  ================  ==============================================
 ``um``        Maintained        ``x86_64`` only.
 ============  ================  ==============================================
+