Revert of Internalize strings in-place

src/runtime/runtime-i18n.cc

Index: src/runtime/runtime-i18n.cc
diff --git a/src/runtime/runtime-i18n.cc b/src/runtime/runtime-i18n.cc
index ce2650727a24d48c12aa612ffdd9c7c5d09937cf..1caf4cc1987a4a00b6630f3763dc92552a5d7df1 100644
--- a/src/runtime/runtime-i18n.cc
+++ b/src/runtime/runtime-i18n.cc
@@ -865,8 +865,6 @@ MUST_USE_RESULT Object* LocaleConvertCase(Handle<String> s, Isolate* isolate,
   Handle<SeqTwoByteString> result;
   std::unique_ptr<uc16[]> sap;
 
-  if (dest_length == 0) return isolate->heap()->empty_string();
-
   // This is not a real loop. It'll be executed only once (no overflow) or
   // twice (overflow).
   for (int i = 0; i < 2; ++i) {
@@ -1075,7 +1073,7 @@ MUST_USE_RESULT Object* ConvertToLower(Handle<String> s, Isolate* isolate) {
 
 MUST_USE_RESULT Object* ConvertToUpper(Handle<String> s, Isolate* isolate) {
   int32_t length = s->length();
-  if (s->HasOnlyOneByteChars() && length > 0) {
+  if (s->HasOnlyOneByteChars()) {
     Handle<SeqOneByteString> result =
         isolate->factory()->NewRawOneByteString(length).ToHandleChecked();