Remove various empty or useless functions

In particular remove init()/destroy() functions that do nothing, or
destroy functions that only free memory.

src/fish.cpp

@@ -376,11 +376,9 @@ int main(int argc, char **argv) {
     const struct config_paths_t paths = determine_config_directory_paths(argv[0]);
     env_init(&paths);
     proc_init();
-    event_init();
     builtin_init();
     misc_init();
     reader_init();
-    history_init();
 
     parser_t &parser = parser_t::principal_parser();
 
@@ -448,11 +446,8 @@ int main(int argc, char **argv) {
         parser.emit_profiling(s_profiling_output_filename);
     }
 
-    history_destroy();
+    history_save_all();
     proc_destroy();
-    builtin_destroy();
-    reader_destroy();
-    event_destroy();
     exit_without_destructors(exit_status);
     return EXIT_FAILURE;  // above line should always exit
 }