Remove unused constants

When compiling protobuf these produce warnings

src/google/protobuf/compiler/cpp/cpp_helpers.cc

@@ -66,7 +66,6 @@ namespace {
 
 static const char kAnyMessageName[] = "Any";
 static const char kAnyProtoFile[] = "google/protobuf/any.proto";
-static const char kGoogleProtobufPrefix[] = "google/protobuf/";
 
 std::string DotsToColons(const std::string& name) {
   return StringReplace(name, ".", "::", true);

src/google/protobuf/compiler/java/java_helpers.cc

@@ -91,8 +91,6 @@ const std::unordered_set<string>* kReservedNames =
         "transient",  "try",          "void",      "volatile",   "while",
     });
 
-const int kDefaultLookUpStartFieldNumber = 40;
-
 bool IsForbidden(const std::string& field_name) {
   for (int i = 0; i < GOOGLE_ARRAYSIZE(kForbiddenWordList); ++i) {
     if (field_name == kForbiddenWordList[i]) {