Fix FGVCAircraft dataset documentation (#5814)
Fix FGVCAircraft dataset documentation (#5814)

There is a mistake in FGVCAircraft dataset documentation. If you load dataset and sum up 'trainval' and 'test' splits, there are not 10 200, but 10 000 images. Also mistake is in the number of classes: if we choose `annotation_level` to be `variant`, then unique number of classes is going to be not 102, but 100, and with `manufacturer` level it is not 41, but 30.

Co-authored-by: Nicolas Hug <1a73af9e7ae00182733b2292511b814be66f065f@nicolas-hug.com>
pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision