Arrow: Deprecate unused fixed width binary reader classes

[wypoon]

For fixed width binary, the FixedSizeBinaryXXX readers are actually used.
In VectorizedArrowReader::read:

          case UUID:
          case FIXED_WIDTH_BINARY:
          case FIXED_LENGTH_DECIMAL:
            vectorizedColumnIterator
                .fixedSizeBinaryBatchReader()
                .nextBatch(vec, typeWidth, nullabilityHolder);
            break;

This is a follow-up to #11276.

[wypoon]

I saw in my IDE that this method is never called, which means that the chain of fixed width binary reader classes are never used.

[wypoon]

@nastra I missed noticing earlier that the fixed width binary reader classes are no longer used.
I think this is it, though.

[nastra]

I don't think we can just remove this. We should add a deprecation message (@deprecated since 1.7.0, will be removed in 1.8.0) here and to fixedWidthTypeBinaryBatchReaderas it's possible that consumers of Iceberg could use this. See also #3249 on how we did the deprecation and #7987 later removed this

[wypoon]

Ok, I will deprecate rather than remove the unused code.
There was no revapi failure, so I thought the removal was ok.
In any case, it's a useful exercise to show that with the code removed, the build and all tests still pass.