Python: Revert IterableSequenceNode as LocalSourceNode

When looking things over a bit more, we could actually exclude the steps
that would never be used instead. A much more involved solution, but
more performance oriented and clear in terms of what is supported (at
least until we start supporting type-tracking with more than depth 1
access-path, if that ever happens)

python/ql/consistency-queries/TypeTrackingConsistency.ql

@@ -27,10 +27,6 @@ private module ConsistencyChecksInput implements ConsistencyChecksInputSig {
       TypeTrackingInput::simpleLocalSmallStep*(m, n)
     )
     or
-    // TODO: when adding support for proper content, handle iterable unpacking better
-    // such as `for k,v in items:`, or `a, (b,c) = ...`
-    n instanceof DataFlow::IterableSequenceNode
-    or
     // We have missing use-use flow in
     // https://github.com/python/cpython/blob/0fb18b02c8ad56299d6a2910be0bab8ad601ef24/Lib/socketserver.py#L276-L303
     // which I couldn't just fix. We ignore the problems here, and instead rely on the