Remove a redundant /XObject stream dictionary objId check in PartialEvaluator.hasBlendModes (PR 6971 follow-up)

This case should no longer happen, given the `instanceof Ref` branch just above (added in PR 6971).
Also, I've run the entire test-suite locally with `continue` replaced by `throw new Error(...)` and didn't find any problems.

src/core/evaluator.js

@@ -328,9 +328,6 @@ class PartialEvaluator {
           continue;
         }
         if (xObject.dict.objId) {
-          if (processed[xObject.dict.objId]) {
-            continue; // Stream has objId and was processed already.
-          }
           processed[xObject.dict.objId] = true;
         }
         var xResources = xObject.dict.get("Resources");