Remove "include sstream" from command_line_interface.cc

src/google/protobuf/compiler/command_line_interface.cc

@@ -46,7 +46,6 @@
 #endif
 #include <errno.h>
 #include <iostream>
-#include <sstream>
 #include <ctype.h>
 
 #include <google/protobuf/stubs/hash.h>