[rand.device] Remove stray \textit.

Fixes #6513.

Author: Eelis

source/numerics.tex

@@ -3631,7 +3631,7 @@
     // property functions
     double entropy() const noexcept;
 
-    @\textit{// no copy functions}@
+    // no copy functions
     random_device(const random_device&) = delete;
     void operator=(const random_device&) = delete;
   };