Drop non-english manuals

Index: dist/unix/CMakeLists.txt
--- dist/unix/CMakeLists.txt.orig
+++ dist/unix/CMakeLists.txt
@@ -20,7 +20,6 @@ endif()
 
 set(manPageLanguages
     en
-    ru
 )
 
 foreach(manPageLanguage ${manPageLanguages})
