[mlir][MemRefToLLVM] Remove the code for lowering collaspe/expand_shape

collapse/expand_shape are supposed to be expanded before we hit the
lowering code.
The expansion is done with the pass called expand-strided-metadata.

This patch is NFC in spirit but not in practice because
expand-strided-metadata won't try to accomodate for "invalid" strides
for dynamic sizes that are 1 at runtime.

The previous code was broken in that respect too, but differently: it
handled only the case of row-major layouts.
That whole part is being reworked separately.

Differential Revision: https://reviews.llvm.org/D136483