Remove some varSetElems in dsCmdStmt
Remove some varSetElems in dsCmdStmt

varSetElems introduces unnecessary determinism and it's easy to
preserve determinism here.

Test Plan: ./validate

Reviewers: goldfire, simonmar, austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2195

GHC Trac Issues: #4012

(cherry picked from commit 0e719885f53e20f2e14a94b32d858b47b516a8fc)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc