[SeparateConstOffsetFromGEP] make two tests more strict

inbounds are not necessary in these two tests. zext(a +nuw b) = zext(a) +
zext(b) should hold with or without inbounds.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210437 91177308-0d34-0410-b5e6-96231b3b80d8