Remove an assert from visitForwardedGuaranteedOperands

Some guaranteed forwarding instructions have multiple operands:
mark_dependence, ref_to_bridge_object.

The corresponding instruction types checked here already have
documentation that the forwarded operand is the first operand. The
assert is overly cautious, and checking for indiviudal opcodes would be
tedious maintenance.

(cherry picked from commit 2d92af4)

Author: atrick

lib/SIL/Utils/OwnershipUtils.cpp

@@ -1779,8 +1779,6 @@ bool swift::visitForwardedGuaranteedOperands(
       || isa<OwnershipForwardingMultipleValueInstruction>(inst)
       || isa<MoveOnlyWrapperToCopyableValueInst>(inst)
       || isa<CopyableToMoveOnlyWrapperValueInst>(inst)) {
-    assert(inst->getNumRealOperands() == 1
-           && "forwarding instructions must have a single real operand");
     assert(!isa<SingleValueInstruction>(inst)
            || !BorrowedValue(cast<SingleValueInstruction>(inst))
                   && "forwarded operand cannot begin a borrow scope");