[lldb][test] Check the sp lookup in register sets that have no rsp (#229401)
Since llvm#223857, `GetIndexOfChildWithName("sp")` in a set holding the
architectural sp but not rsp (Windows "supplementary registers") finds
that sp, but the early continue from llvm#226176 skips those sets, so
the else block asserting it never ran.
This patch drops it and compares against "esp" on i386, where sp shares
a set with esp and the continue was what kept the else branch from
failing. x86_64 sets that hold rsp are checked as before.