Assembler: Rewrite test for function-local metadata

This test for function-local metadata did strange things, and never
really sent in valid arguments for `llvm.dbg.declare` and
`llvm.dbg.value` intrinsics.  Those that might have once been valid have
bitrotted.

Rewrite it to be a targeted test for function-local metadata --
unrelated to debug info, which is tested elsewhere -- and rename it to
better match other metadata-related tests.

(Note: the scope of function-local metadata changed drastically during
the metadata/value split, but I didn't properly clean up this testcase.
Most of the IR in this file, while invalid for debug info intrinsics,
used to provide coverage for various (now illegal) forms of
function-local metadata.)

llvm-svn: 232290