The check that an instruction is in the same function as its operands is
hopefully redundant and can be removed. Just to be sure, I've added the
check to a sanity query.
This check turned out to cause bad performance in the alias analysis
because it got inlined into `AliasAnalysis::resultEscapes` and then
pulled out to a loop-invariant predicate that got a bad join order. With
this check removed, the `ssa/AliasAnalysis.qll` file is orders of
magnitude faster.
