Revert build of pdfium_unittests.

pdfium.gyp

 {
   'variables': {
     'pdf_use_skia%': 0,
   },
   'target_defaults': {
     'defines' : [
       'FT2_BUILD_LIBRARY',
       '_FPDFSDK_LIB',
       '_NO_GDIPLUS_',  # workaround text rendering issues on Windows
       'OPJ_STATIC',
@@ skipping 784 matching lines @@
         'fpdfsdk/src/formfiller/FFL_FormFiller.cpp',
         'fpdfsdk/src/formfiller/FFL_IFormFiller.cpp',
         'fpdfsdk/src/formfiller/FFL_ListBox.cpp',
         'fpdfsdk/src/formfiller/FFL_Notify.cpp',
         'fpdfsdk/src/formfiller/FFL_PushButton.cpp',
         'fpdfsdk/src/formfiller/FFL_RadioButton.cpp',
         'fpdfsdk/src/formfiller/FFL_TextField.cpp',
         'fpdfsdk/src/formfiller/FFL_Utils.cpp',
       ],
     },
-    {
-      'target_name': 'pdfium_unittests',
-      'type': 'executable',
-      'dependencies': [
-        '../../base/base.gyp:base',
-        '../../base/base.gyp:run_all_unittests',
-        '../../base/base.gyp:test_support_base',
-        '../../testing/gtest.gyp:gtest',
-        'pdfium',
-      ],
-      'include_dirs': [
-        '<(DEPTH)'
-      ],
-      'sources': [
-        'core/src/fxcrt/fx_basic_bstring_unittest.cpp',
-      ],
-    }
   ],
 }