[swappable.requirements] Remove inappropriate \tcode from 'swappable'

Author: tkoeppe

source/lib-intro.tex

@@ -1598,7 +1598,7 @@
 \tcode{u.\~T()} &   All resources owned by \tcode{u} are reclaimed, no exception is propagated. \\
 \end{concepttable}
 
-\rSec3[swappable.requirements]{\tcode{Swappable} requirements}
+\rSec3[swappable.requirements]{Swappable requirements}
 
 \pnum
 This subclause provides definitions for swappable types and expressions. In these