Replace HiCBricks with rhdf5 in getChrCGFromCools

The vignette build was segfaulting in H5close() called from HiCBricks::Create_many_Bricks_from_mcool. Reading mcool files directly via rhdf5 (already a dependency) avoids the crash and removes HiCBricks as a dependency entirely.

Verified output matches cgEx exactly (all.equal: TRUE).