[styles] Remove version check for listings package

This check breaks every time there is a new version, and is perhaps
not pulling its weight.

Author: tkoeppe

source/styles.tex

@@ -142,14 +142,6 @@
 %% (copied verbatim from listings.sty version 1.6 except where commented)
 \makeatletter
 
-\lst@CheckVersion{1.8d}{\lst@CheckVersion{1.8c}{\lst@CheckVersion{1.8b}{\lst@CheckVersion{1.7}{\lst@CheckVersion{1.6}{\lst@CheckVersion{1.5b}{
- \typeout{^^J%
- ***^^J%
- *** This file requires listings.sty version 1.6.^^J%
- *** You have version \lst@version; exiting ...^^J%
- ***^^J}%
- \batchmode \@@end}}}}}}
-
 \def\lst@Init#1{%
     \begingroup
     \ifx\lst@float\relax\else