[mlir][linalg][nfc] Clean-up leftover code post #149156 (#151334)

In #149156, I ensured that we
no longer generate spurious `tensor.empty` ops when vectorizing
`linalg.unpack`.

This follow-up removes leftover code that is now redundant but was
missed in the original PR and in #150602 that was also meant to clean-up
left-over code.

Note, this is removing code to compute "write-vector-sizes". Instead,
these are fully inferred from previous Ops.

Author: banach-space

mlir/lib/Dialect/Linalg/Transforms/Vectorization.cpp

@@ -1946,12 +1946,6 @@ vectorizeAsTensorUnpackOp(RewriterBase &rewriter, linalg::UnPackOp unpackOp,
   vector::ShapeCastOp shapeCastOp = vector::ShapeCastOp::create(
       rewriter, loc, vecCollapsedType, transposeOp->getResult(0));
 
-  // writeVectorSizes had to match the shapecast shape for dynamic sizes,
-  // otherwise the validator complains that the mask size is invalid.
-  SmallVector<int64_t> writeVectorSizes(
-      unpackOp.getDestType().hasStaticShape()
-          ? vectorSizes
-          : shapeCastOp.getResultVectorType().getShape());
   Operation *write = createWriteOrMaskedWrite(
       rewriter, loc, shapeCastOp.getResult(), unpackOp.getDest(),
       /*writeIndices=*/{}, useInBoundsInsteadOfMasking);