AllocOp: drop redundant verifier check

The equality check between the rank of a memref and the input size of the
layout affine map in AllocOp::verify is subsumed by the well-formedness check
of the memref type itself.  Drop the redundant check from the verifier since it
is never exercised (the type builder does not allow one to construct a type
that would not pass the verifier check).

PiperOrigin-RevId: 256551247