Revert "Update isl to isl-0.24-69-g54aac5ac"

This reverts commit 13f95cc3d10d9884acd2dbfc112e3c7079403c0a.

The commit makes some polly tests failing

GitOrigin-RevId: 2ae7d6d42741347346d9760f6243b72a4a0c343f
20 files changed