Python: Fix bad join order in py/ineffectual-statement.

[tausbn]

This used to take 30s on cpython.

Tuple counts for StatementNoEffect::side_effecting_binary#f:
46522     ~0%     {2} r1 = ClassObject::ClassObject::hasAttribute_dispred#fb AS L AND NOT StatementNoEffect::side_effecting_binary#f#antijoin_rhs AS R(L.<0>, L.<1>)
46522     ~2%     {2} r2 = SCAN r1 OUTPUT r1.<1>, r1.<0>
950960    ~2%     {2} r3 = JOIN r2 WITH Operations::Operator::getSpecialMethodName_dispred#ff_10#join_rhs AS R ON FIRST 1 OUTPUT R.<1>, r2.<1>
950960    ~2%     {2} r4 = JOIN r3 WITH py_operators AS R ON FIRST 1 OUTPUT R.<2>, r3.<1>
950960    ~0%     {3} r5 = JOIN r4 WITH AstGenerated::BinaryExpr_::getLeft_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r4.<1>, r4.<0>
122934382 ~0%     {2} r6 = JOIN r2 WITH Operations::Cmpop::getSpecialMethodName_dispred#ff_10#join_rhs AS R ON FIRST 1 OUTPUT R.<1>, r2.<1>
122934382 ~3%     {3} r7 = JOIN r6 WITH project#Operations::Compare::compares_dispred#ffff#3_201#join_rhs AS R ON FIRST 1 OUTPUT R.<2>, r6.<1>, R.<1>
123885342 ~3%     {3} r8 = r5 \/ r7
300       ~8%     {1} r9 = JOIN r8 WITH project#Exprs::Expr::refersTo_dispred#ffff AS R ON FIRST 2 OUTPUT r8.<2>
                  return r9

With this commit, it takes a few milliseconds.

[tausbn]

Performance comparison here: https://git.semmle.com/gist/taus/7abb4c6b661e45006037ff0f4f9df39b
Not a huge improvement, but still, every little helps.

[RasmusWL]

Magic ✨