Remove install target for non-existant directory.

--- a/src/CMakeLists.txt	2015-09-13 20:52:28.517344327 +0200
+++ b/src/CMakeLists.txt	2015-09-13 20:53:04.842453987 +0200
@@ -122,12 +122,6 @@
 		DESTINATION
 			${CMAKE_INSTALL_PREFIX}/share/applications
 	)
-	install(
-		FILES
-			${MARS_SOURCE_DIR}/resources/mars
-		DESTINATION
-			${CMAKE_INSTALL_PREFIX}/share/menu
-	)
 
 else(UNIX)
 	# executable
