[core] remove some uses of <iostream> and <sstream>

src/mbgl/storage/response.cpp

@@ -1,8 +1,4 @@
 #include <mbgl/storage/response.hpp>
-#include <mbgl/util/chrono.hpp>
-
-#include <iostream>
-#include <cassert>
 
 namespace mbgl {
 
@@ -26,25 +22,4 @@ Response::Error::Error(Reason reason_, std::string message_, optional<Timestamp>
     : reason(reason_), message(std::move(message_)), retryAfter(std::move(retryAfter_)) {
 }
 
-std::ostream& operator<<(std::ostream& os, Response::Error::Reason r) {
-    switch (r) {
-    case Response::Error::Reason::Success:
-        return os << "Response::Error::Reason::Success";
-    case Response::Error::Reason::NotFound:
-        return os << "Response::Error::Reason::NotFound";
-    case Response::Error::Reason::Server:
-        return os << "Response::Error::Reason::Server";
-    case Response::Error::Reason::Connection:
-        return os << "Response::Error::Reason::Connection";
-    case Response::Error::Reason::RateLimit:
-        return os << "Response::Error::Reason::RateLimit";
-    case Response::Error::Reason::Other:
-        return os << "Response::Error::Reason::Other";
-    }
-
-    // The above switch is exhaustive, but placate GCC nonetheless:
-    assert(false);
-    return os;
-}
-
 } // namespace mbgl