remove assertion that triggers for PRENV

com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/data/RPromise.java

@@ -238,7 +238,6 @@ public class RPromise extends RObject implements RTypedValue {
      * @see #execFrame
      */
     public final MaterializedFrame getFrame() {
-        assert !isEvaluated();
         return execFrame;
     }