Drop MemRefUtils from the ExecutionEngine

The ExecutionEngine was updated recently to only take the LLVM dialect as
input. Memrefs are no longer expected in the signature of the entry point
function by the executor so there is no need to allocate and free them. The
code in MemRefUtils is therefore dead and furthermore out of sync with the
recent evolution of memref type to support strides. Drop it.

PiperOrigin-RevId: 276272302