Remove: OS/2 port

src/os/unix/CMakeLists.txt

@@ -1,12 +1,12 @@
 add_files(
     crashlog_unix.cpp
     survey_unix.cpp
-    CONDITION UNIX AND NOT APPLE AND NOT OPTION_OS2
+    CONDITION UNIX AND NOT APPLE
 )
 
 add_files(
     unix.cpp
-    CONDITION UNIX AND NOT OPTION_OS2
+    CONDITION UNIX
 )
 
 add_files(
@@ -14,6 +14,6 @@ add_files(
     CONDITION Fontconfig_FOUND
 )
 
-if(UNIX AND NOT APPLE AND NOT OPTION_OS2)
+if(UNIX AND NOT APPLE)
     target_sources(openttd PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/unix_main.cpp)
 endif()