tools/gn: Remove code for forward_dependent_configs_from variable.

tools/gn/builder.cc

Index: tools/gn/builder.cc
diff --git a/tools/gn/builder.cc b/tools/gn/builder.cc
index ca11e888d353bd3d6c5168afe09580103711fab8..25f6893cc18f1b68ff44aa843a572831a68ef831 100644
--- a/tools/gn/builder.cc
+++ b/tools/gn/builder.cc
@@ -495,15 +495,6 @@ bool Builder::ResolveForwardDependentConfigs(Target* target, Err* err) {
         break;
       }
     }
-    if (!config.ptr) {
-      *err = Err(target->defined_from(),
-          "Target in forward_dependent_configs_from was not listed in the deps",
-          "This target has a forward_dependent_configs_from entry that was "
-          "not present in\nthe deps. A target can only forward things it "
-          "depends on. It was forwarding:\n  " +
-          config.label.GetUserVisibleName(false));
-      return false;
-    }
   }
   return true;
 }