Remove unnecessary null check, instanceof handles it

Author: Col-E

javaparser-core/src/main/java/com/github/javaparser/ast/Node.java

@@ -339,7 +339,7 @@ public final int hashCode() {
 
  @Override
  public boolean equals(final Object obj) {
- if (obj == null || !(obj instanceof Node)) {
+ if (!(obj instanceof Node)) {
  return false;
  }
  return EqualsVisitor.equals(this, (Node) obj);