remove SkStippleMaskFilter - no external clients

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': [
       'animator/SkAnimator.h',
@@ skipping 123 matching lines @@
       'effects/SkMagnifierImageFilter.h',
       'effects/SkMatrixConvolutionImageFilter.h',
       'effects/SkMergeImageFilter.h',
       'effects/SkMorphologyImageFilter.h',
       'effects/SkOffsetImageFilter.h',
       'effects/SkPaintFlagsDrawFilter.h',
       'effects/SkPerlinNoiseShader.h',
       'effects/SkPixelXorXfermode.h',
       'effects/SkPorterDuff.h',
       'effects/SkRectShaderImageFilter.h',
-      'effects/SkStippleMaskFilter.h',
       'effects/SkTableColorFilter.h',
       'effects/SkTableMaskFilter.h',
       'effects/SkTestImageFilters.h',
       'effects/SkTransparentShader.h',
       'effects/SkXfermodeImageFilter.h',
       'gpu/GrAARectRenderer.h',
       'gpu/GrBackendEffectFactory.h',
       'gpu/GrClipData.h',
       'gpu/GrColor.h',
       'gpu/GrConfig.h',
@@ skipping 115 matching lines @@
       'views/unix/keysym2ucs.h',
       'xml/SkBML_WXMLParser.h',
       'xml/SkBML_XMLParser.h',
       'xml/SkDOM.h',
       'xml/SkJS.h',
       'xml/SkXMLParser.h',
       'xml/SkXMLWriter.h',
     ],
   },
 }