[SIL] computeDominatedBoundaryBlocks on non-OSSA.

The algorithm requires no critical edges, but that doesn't mean
require ownership.  Remove the assert to allow the utility to be called
from code where the caller has manually split edges.

In the fullness of time, there should no passes should introduce
critical edges.

Author: nate-chandler

include/swift/SIL/Dominance.h

@@ -94,7 +94,7 @@ class DominanceInfo : public DominatorTreeBase {
 
 /// Compute a single block's dominance frontier.
 ///
-/// Precondition: no critical edges (OSSA)
+/// Precondition: no critical edges
 ///
 /// Postcondition: each block in \p boundary is dominated by \p root and either
 /// exits the function or has a single successor which has a predecessor that is

lib/SIL/Utils/Dominance.cpp

@@ -145,8 +145,6 @@ void PostDominanceInfo::verify() const {
 void swift::computeDominatedBoundaryBlocks(
     SILBasicBlock *root, DominanceInfo *domTree,
     SmallVectorImpl<SILBasicBlock *> &boundary) {
-  auto *function = root->getParent();
-  assert(function->hasOwnership());
   assert(boundary.empty());
 
   DominanceOrder domOrder(root, domTree);