Remove IFDE_TxtEdt interfaces where possible.

BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_config") {
   cflags = []
@@ skipping 912 matching lines @@
       "xfa/fee/fde_txtedtengine.cpp",
       "xfa/fee/fde_txtedtengine.h",
       "xfa/fee/fde_txtedtpage.cpp",
       "xfa/fee/fde_txtedtpage.h",
       "xfa/fee/fde_txtedtparag.cpp",
       "xfa/fee/fde_txtedtparag.h",
       "xfa/fee/fx_wordbreak/fx_wordbreak.h",
       "xfa/fee/fx_wordbreak/fx_wordbreak_impl.cpp",
       "xfa/fee/fx_wordbreak/fx_wordbreak_impl.h",
       "xfa/fee/fx_wordbreak/fx_wordbreakdata.cpp",
-      "xfa/fee/ifde_txtedtbuf.h",
       "xfa/fee/ifde_txtedtengine.h",
       "xfa/fee/ifde_txtedtpage.h",
       "xfa/fgas/crt/fgas_algorithm.cpp",
       "xfa/fgas/crt/fgas_algorithm.h",
       "xfa/fgas/crt/fgas_codepage.cpp",
       "xfa/fgas/crt/fgas_codepage.h",
       "xfa/fgas/crt/fgas_encode.cpp",
       "xfa/fgas/crt/fgas_language.h",
       "xfa/fgas/crt/fgas_memory.cpp",
       "xfa/fgas/crt/fgas_memory.h",
@@ skipping 754 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }