This PR removes one OpRewritePattern `shape_cast(shape_cast(x)) -> x`
that is already handled by `ShapeCastOp::fold`.
Note that this might affect downstream users who indirectly call
`populateShapeCastFoldingPatterns(RewritePatternSet &patterns,
PatternBenefit)` and then use `patterns` with a `GreedyRewriteConfig
config` that has `config.fold = false`. (only user I've checked is IREE,
that never uses config.fold = false).