Mac: Delete now-dead elastic overscroll code

Source/platform/blink_platform.gyp

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 289 matching lines @@
           # Some of these are used instead of Chromium platform files, see
           # the specific exclusions in the "exclude" list below.
           ['include', 'audio/mac/FFTFrameMac\\.cpp$'],
           ['include', 'fonts/mac/GlyphPageTreeNodeMac\\.cpp$'],
           ['include', 'mac/ColorMac\\.mm$'],
           ['include', 'mac/BlockExceptions\\.mm$'],
           ['include', 'mac/KillRingMac\\.mm$'],
           ['include', 'mac/LocalCurrentGraphicsContext\\.mm$'],
           ['include', 'mac/NSScrollerImpDetails\\.mm$'],
           ['include', 'mac/ScrollAnimatorMac\\.mm$'],
-          ['include', 'mac/ScrollElasticityController\\.mm$'],
           ['include', 'mac/ThemeMac\\.h$'],
           ['include', 'mac/ThemeMac\\.mm$'],
           ['include', 'mac/WebCoreNSCellExtras\\.h$'],
           ['include', 'mac/WebCoreNSCellExtras\\.mm$'],
  
           # Mac uses only ScrollAnimatorMac.
           ['exclude', 'scroll/ScrollbarThemeNonMacCommon\\.(cpp|h)$'],
           ['exclude', 'scroll/ScrollAnimatorNone\\.cpp$'],
           ['exclude', 'scroll/ScrollAnimatorNone\\.h$'],
 
@@ skipping 137 matching lines @@
           ['OS=="android"', {
             'cflags!': ['-mthumb'],
           }],
         ],
       },{  # target_arch!="arm"
         'type': 'none',
       }],
     ],
   }],
 }