Remove an outdated comment; NFC

StandardConversionSequence is significantly larger than a word.

Author: AaronBallman

clang/include/clang/Sema/Overload.h

@@ -257,10 +257,7 @@ class Sema;
   /// sequence (C++ 13.3.3.1.1). A standard conversion sequence
   /// contains between zero and three conversions. If a particular
   /// conversion is not needed, it will be set to the identity conversion
-  /// (ICK_Identity). Note that the three conversions are
-  /// specified as separate members (rather than in an array) so that
-  /// we can keep the size of a standard conversion sequence to a
-  /// single word.
+  /// (ICK_Identity).
   class StandardConversionSequence {
   public:
     /// First -- The first conversion can be an lvalue-to-rvalue