[turbofan] Remove dead code (related to the SeqStringChar lowering removal).

src/compiler/access-builder.h

Index: src/compiler/access-builder.h
diff --git a/src/compiler/access-builder.h b/src/compiler/access-builder.h
index ae366ccb2e40a595ec9b8c0e24d60a35d45e415c..8e154ff390418e51d55527ca9bd3615793b44f7f 100644
--- a/src/compiler/access-builder.h
+++ b/src/compiler/access-builder.h
@@ -103,9 +103,6 @@ class AccessBuilder final : public AllStatic {
   static ElementAccess ForTypedArrayElement(ExternalArrayType type,
                                             bool is_external);
 
-  // Provides access to the characters of sequential strings.
-  static ElementAccess ForSeqStringChar(String::Encoding encoding);
-
   // ===========================================================================
   // Access to global per-isolate variables (based on external reference).