improved OptionSet.remove's code style

Author: JacobMao

stdlib/public/core/OptionSet.swift

@@ -287,9 +287,12 @@ extension OptionSet where Element == Self {
   @discardableResult
   public mutating func remove(_ member: Element) -> Element? {
     let intersectionElements = intersection(member)
-    let r = !intersectionElements.isEmpty ? Optional(intersectionElements) : nil
+    guard !intersectionElements.isEmpty else {
+      return nil
+    }
+    
     self.subtract(member)
-    return r
+    return intersectionElements
   }
 
   /// Inserts the given element into the set.