XFA: revert bb1405d - Create pdfium_unittests binary.

BUILD.gn

 # Copyright 2014 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.
 
 pdf_use_skia = false
 
 config("pdfium_config") {
   cflags = []
   include_dirs = [
     "third_party/freetype/include"
@@ skipping 1522 matching lines @@
     "//v8",
     "//v8/include",
   ]
   public_deps = [
     "//v8",
   ]
   deps = [
     "//v8:v8_libplatform",
   ]
 }
-
-executable("pdfium_unittests") {
-  testonly = true
-  sources = [
-    "core/src/fxcrt/fx_basic_bstring_unittest.cpp",
-  ]
-  deps = [
-    ":pdfium",
-    "//base",
-    "//base/test:run_all_unittests",
-    "//testing/gtest",
-  ]
-}