[Sema] Remove a check for SequenceExpr in pre-check

This is no longer needed now that we fold
SequenceExpr during the pre-walk.

Author: hamishknight

lib/Sema/PreCheckExpr.cpp

@@ -1244,9 +1244,6 @@ namespace {
           return parent;
         };
         if (auto *parent = takeNextParent()) {
-          if (isa<SequenceExpr>(parent))
-            return finish(true, expr);
-
           SourceLoc lastInnerParenLoc;
           // Unwrap to the outermost paren in the sequence.
           // e.g. `foo(((&bar))`