[Gardening] OSSACanOwned: Removed dead friend.

There's no longer a DenseMap of Defs, so no corresponding DenseMapInfo.

Author: nate-chandler

include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h

@@ -340,7 +340,6 @@ class CanonicalizeOSSALifetime final {
       llvm_unreachable("covered switch");
     }
   };
-  friend llvm::DenseMapInfo<Def>;
 
   /// The defs derived from currentDef whose uses are added to liveness.
   SmallVector<Def, 8> discoveredDefs;