remove a couple unnecessary gems
remove a couple unnecessary gems

- uuidtools is no longer a dependency of aws-sdk-v1
- subexec is no longer a dependency of mini_magick

refs CNVS-34084

test plan: specs should pass

Change-Id: I639b6b4e5c009d00afec4d9c0ed6ec5f9d087f70
Reviewed-on: https://gerrit.instructure.com/98683
Tested-by: Jenkins
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
QA-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

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