remove SkStippleMaskFilter - no external clients

gyp/gmslides.gypi

 # include this gypi to include all the golden master slides.
 {
   'include_dirs': [
     '../gm',
     # include dirs needed by particular GMs
     '../src/utils/debugger',
     '../src/images',
     '../src/lazy',
   ],
   'conditions': [
@@ skipping 130 matching lines @@
         '../gm/pictureshadertile.cpp',
         '../gm/points.cpp',
         '../gm/poly2poly.cpp',
         '../gm/polygons.cpp',
         '../gm/quadpaths.cpp',
         '../gm/rects.cpp',
         '../gm/resizeimagefilter.cpp',
         '../gm/rrect.cpp',
         '../gm/rrects.cpp',
         '../gm/roundrects.cpp',
-        '../gm/samplerstress.cpp',
         # '../gm/scalebitmap.cpp',
         '../gm/shaderbounds.cpp',
         '../gm/selftest.cpp',
         '../gm/shadertext.cpp',
         '../gm/shadertext2.cpp',
         '../gm/shadertext3.cpp',
         '../gm/shadows.cpp',
         '../gm/shallowgradient.cpp',
         '../gm/simpleaaclip.cpp',
         '../gm/skbug1719.cpp',
@@ skipping 66 matching lines @@
         '../gm/shadertext2.cpp',
         '../gm/shadertext3.cpp',
 
         # TODO(reed): Allocates more memory than Android devices are capable of
         # fulfilling. See http://skbug.com/1978
         '../gm/verylargebitmap.cpp',
       ],
     }],
   ],
 }