promoteToSharedAtDepth: do not throw at depth 0

The original implementation was throwing a NYI exception if promotion
was requested at depth 0.  This was due to bandsContainingScheduleDepth
not supporting the depth 0, and is fixed in a5a88f8
(bandsContainingScheduleDepth: support depth 0).  Drop the check and NYI
exception.

Author: ftynse

tc/core/polyhedral/cuda/memory_promotion_heuristic.cc

@@ -584,10 +584,6 @@ void promoteToSharedAtDepth(
     bool unrollCopies) {
   using namespace tc::polyhedral::detail;
 
-  if (depth == 0) {
-    throw promotion::PromotionNYI("promotion before any band");
-  }
-
   auto& scop = mscop.scop();
   auto root = scop.scheduleRoot();