Don't copy ids when creating trivial assumptions

When creating an assumption from an assertion, don't copy the id if the
resulting assumption is trivial (such as when subsumption is turned
off).

Source/VCGeneration/VCGen.cs

@@ -58,9 +58,12 @@ public static AssumeCmd AssertTurnedIntoAssume(VCGenOptions options, AssertCmd a
       }
 
       var assume = new AssumeCmd(assrt.tok, expr);
-      // Copy any {:id ...} from the assertion to the assumption, so
-      // we can track it while analyzing verification coverage.
-      (assume as ICarriesAttributes).CopyIdFrom(assrt.tok, assrt);
+      if (expr != Expr.True) {
+        // Copy any {:id ...} from the assertion to the assumption, so
+        // we can track it while analyzing verification coverage. But
+        // skip it if it's `true` because that's never useful to track.
+        (assume as ICarriesAttributes).CopyIdFrom(assrt.tok, assrt);
+      }
       return assume;
     }