Drop support for memrefs from JitRunner

The support for functions taking and returning memrefs of floats was introduced
in the first version of the runner, created before MLIR had reliable lowering
of allocation/deallocation to library calls.  It forcibly runs MLIR
transformation convering affine, loop and standard dialects into the LLVM
dialect, unlike the other runner flows that accept the LLVM dialect directly.
Memref support leads to more complex layering and is generally fragile.  Drop
it in favor of functions returning a scalar, or library-based function calls to
print memrefs and other data structures.

PiperOrigin-RevId: 271330839