Reference doesn't allow code voice in abstract.

Fixes <rdar://86212313>

Author: amartini51

stdlib/public/core/Optional.swift

@@ -10,8 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-/// A type that represents either a wrapped value or `nil`, the absence of a
-/// value.
+/// A type that represents either a wrapped value the absence of a value.
 ///
 /// You use the `Optional` type whenever you use optional values, even if you
 /// never type the word `Optional`. Swift's type system usually shows the