Remove <iostream> from the common.h header (#14174)

<iostream> embeds a global constructor (to initialize std::cout and such), typically `static ios_base::Init __ioinit;` in libstdc++).

This header is not directly necessary in the common header and has a small impact on every compilation unit that includes it.

As an example, removing that header dependency in turns suppresses 33 global constructors from the firefox core library libxul.

Closes #14174

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/14174 from serge-sans-paille:feature/remove-iostream-from-common d3a6be6ee4
PiperOrigin-RevId: 568626744

src/google/protobuf/stubs/common.h

@@ -13,7 +13,6 @@
 #define GOOGLE_PROTOBUF_COMMON_H__
 
 #include <algorithm>
-#include <iostream>
 #include <memory>
 #include <string>
 #include <vector>