[fix] Remove non-CRAN packages from Suggests (BPCells, SeuratData)

These GitHub-only packages cause pak dependency resolution to fail in CI.
The code already guards usage with requireNamespace() checks.

Author: mianaz

DESCRIPTION

@@ -77,13 +77,11 @@ Collate:
     'h5Seurat_bindings.R'
 Suggests:
     BiocGenerics,
-    BPCells,
     formatR,
     httr,
     knitr,
     reticulate,
     rmarkdown,
-    SeuratData,
     SingleCellExperiment,
     SummarizedExperiment,
     testthat (>= 3.0.0)