Revert "[ast] Add a Flatten method for AstConsString"

This reverts commit 7a0ae73b.

Reason for revert: Not useful after all, no tests, we can reland if we
do end up needing it.

Original change's description:
> [ast] Add a Flatten method for AstConsString
> 
> This allows off-thread flattening.
> 
> Bug: chromium:1011762
> Change-Id: If83f7bbcbf74165987a4c157184f5b92dc554971
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1924437
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Toon Verwaest <verwaest@chromium.org>
> Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#65075}

TBR=leszeks@chromium.org,verwaest@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:1011762
Change-Id: Ia72e5abdc9b6149a337565576806427dcd1d11c2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1991484Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65638}

src/ast/ast-value-factory.cc

@@ -250,50 +250,6 @@ AstConsString* AstValueFactory::NewConsString(const AstRawString* str1,
   return NewConsString()->AddString(zone_, str1)->AddString(zone_, str2);
 }
 
-const AstRawString* AstValueFactory::Flatten(const AstConsString* str) {
-  if (str->IsEmpty()) return empty_string();
-  AstConsString::Segment segment = str->segment_;
-  if (!segment.next) return segment.string;
-
-  int length = segment.string->length();
-  bool is_one_byte = segment.string->is_one_byte();
-  while (segment.next) {
-    segment = *segment.next;
-    length += segment.string->length();
-    is_one_byte &= segment.string->is_one_byte();
-  }
-
-  if (is_one_byte) {
-    Vector<byte> data(zone()->NewArray<byte>(length), length);
-    segment = str->segment_;
-    byte* p = data.begin();
-    while (true) {
-      CopyChars(p, segment.string->raw_data(), segment.string->length());
-      p += segment.string->length();
-      if (!segment.next) break;
-      segment = *segment.next;
-    }
-    return GetOneByteString(data);
-  }
-
-  Vector<uint16_t> data(zone()->NewArray<uint16_t>(length), length);
-  segment = str->segment_;
-  uint16_t* p = data.begin();
-  while (true) {
-    if (segment.string->is_one_byte()) {
-      CopyChars(p, segment.string->raw_data(), segment.string->length());
-    } else {
-      CopyChars(p,
-                reinterpret_cast<const uint16_t*>(segment.string->raw_data()),
-                segment.string->length());
-    }
-    p += segment.string->length();
-    if (!segment.next) break;
-    segment = *segment.next;
-  }
-  return GetTwoByteString(data);
-}
-
 void AstValueFactory::Internalize(Isolate* isolate) {
   // Strings need to be internalized before values, because values refer to
   // strings.

src/ast/ast-value-factory.h

@@ -312,7 +312,6 @@ class AstValueFactory {
   V8_EXPORT_PRIVATE AstConsString* NewConsString(const AstRawString* str);
   V8_EXPORT_PRIVATE AstConsString* NewConsString(const AstRawString* str1,
                                                  const AstRawString* str2);
-  V8_EXPORT_PRIVATE const AstRawString* Flatten(const AstConsString* str);
 
   V8_EXPORT_PRIVATE void Internalize(Isolate* isolate);