spec: remove unused `sequel` gem
spec: remove unused `sequel` gem

refs CNVS-34084

test plan: tests should pass

Change-Id: Idf0e3dde6a76eee2e84533be8eb687f5e1193f86
Reviewed-on: https://gerrit.instructure.com/98548
Tested-by: Jenkins
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
QA-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

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