Fix build with Boost 1.91

Index: src/CMakeLists.txt
--- src/CMakeLists.txt.orig
+++ src/CMakeLists.txt
@@ -248,7 +248,6 @@ if(ENABLE_GAME)
 		Boost::iostreams
 		Boost::program_options
 		Boost::regex
-		Boost::system
 		Boost::random
 		Boost::coroutine
 		Boost::locale
@@ -295,7 +294,6 @@ if(ENABLE_TESTS)
 		Boost::iostreams
 		Boost::program_options
 		Boost::regex
-		Boost::system
 		Boost::random
 		Boost::coroutine
 		Boost::locale
@@ -344,7 +342,6 @@ if(ENABLE_SERVER)
 		Boost::iostreams
 		Boost::program_options
 		Boost::regex
-		Boost::system
 		Boost::random
 		Boost::coroutine
 		Boost::locale
@@ -385,7 +382,6 @@ if(ENABLE_CAMPAIGN_SERVER)
 		Boost::iostreams
 		Boost::program_options
 		Boost::regex
-		Boost::system
 		Boost::random
 		Boost::coroutine
 		Boost::locale
