remove (now unused) Sk64 -- just use int64_t

gyp/public_headers.gypi

 # Include this gypi to include all public header files that exist in the
 # include directory.
 #
 # The list is computed by running 'find include -name *.h' in the root dir of
 # the project.
 #
 {
   'variables': {
     'header_filenames': [
       'pdf/SkPDFDevice.h',
@@ skipping 178 matching lines @@
       'core/SkDocument.h',
       'core/SkInstCnt.h',
       'core/SkEndian.h',
       'core/SkColorTable.h',
       'core/SkBitmap.h',
       'core/SkDraw.h',
       'core/SkPackBits.h',
       'core/SkFloatBits.h',
       'core/SkDeque.h',
       'core/SkTRegistry.h',
-      'core/Sk64.h',
       'core/SkTLazy.h',
       'core/SkComposeShader.h',
       'core/SkUtils.h',
       'core/SkImage.h',
       'core/SkTileGridPicture.h',
       'core/SkPaintOptionsAndroid.h',
       'core/SkDeviceProperties.h',
       'core/SkGraphics.h',
       'core/SkCanvas.h',
       'core/SkPicture.h',
@@ skipping 82 matching lines @@
       'views/unix/XkeysToSkKeys.h',
       'views/SkKey.h',
       'views/SkView.h',
       'views/SkOSMenu.h',
       'views/SkOSWindow_Unix.h',
       'views/SkWidget.h',
       'views/SkOSWindow_Win.h',
     ],
   },
 }