(REF) dev/core#2601 - Cleanup stale parameter

(REF) dev/core#2601 - Cleanup stale parameter

Overview
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This cleans up a parameter that became unused/unnecessary in #20256.

History
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This revision is a little bouncy. Instead of before/after, here's a history:

* `<= v5.36`: `getAllModulePermissions($descriptions = FALSE)`
* `=  v5.37.0`: `getAllModulePermissions($descriptions = FALSE, &$permissions)`
* `>= v.37.1`: `getAllModulePermissions($descriptions = FALSE)`

I grepped `universe` to confirm that no other repos were using the intermediate signature.