[LifetimeCompletion] Enable.

Now that the compile time regressions observed in rdar://132552637 are
fixed, enable completion of lifetimes during the SILGenCleanup.

Author: nate-chandler

include/swift/AST/SILOptions.h

@@ -189,7 +189,7 @@ class SILOptions {
   bool EnableSILOpaqueValues = false;
 
   /// Introduce linear OSSA lifetimes after SILGen
-  bool OSSACompleteLifetimes = false;
+  bool OSSACompleteLifetimes = true;
 
   /// Verify linear OSSA lifetimes throughout OSSA pipeline.
   bool OSSAVerifyComplete = false;