Make documented complexity consistent

Since most of the documentation in the code use O(`self.count`) instead of O(`count`), change the inconsistent code documentation to O(`self.count`).

stdlib/public/core/HashedCollections.swift.gyb

@@ -1078,7 +1078,7 @@ public struct Dictionary<Key : Hashable, Value> :
   ///
   /// Invalidates all indices with respect to `self`.
   ///
-  /// - Complexity: O(`count`).
+  /// - Complexity: O(`self.count`).
   public mutating func removeAtIndex(index: Index) -> Element {
     return _variantStorage.removeAtIndex(index)
   }
@@ -1101,7 +1101,7 @@ public struct Dictionary<Key : Hashable, Value> :
   ///   storage capacity that the collection has, otherwise the underlying
   ///   storage is released.  The default is `false`.
   ///
-  /// Complexity: O(`count`).
+  /// Complexity: O(`self.count`).
   public mutating func removeAll(keepCapacity keepCapacity: Bool = false) {
     // The 'will not decrease' part in the documentation comment is worded very
     // carefully.  The capacity can increase if we replace Cocoa storage with