Remove scons-related files

Externals/libpng/SConscript

@@ -1,28 +0,0 @@
-# -*- python -*-
-
-Import('env')
-import sys
-
-if env.has_key('shared_png') and env['shared_png']:
-	Return()
-
-files = [
-	'png.c',
-	'pngerror.c',
-	'pngget.c',
-	'pngmem.c',
-	'pngpread.c',
-	'pngread.c',
-	'pngrio.c',
-	'pngrtran.c',
-	'pngrutil.c',
-	'pngset.c',
-	'pngtrans.c',
-	'pngwio.c',
-	'pngwrite.c',
-	'pngwtran.c',
-	'pngwutil.c',
-	]
-
-env['CPPPATH'] += ['#Externals/libpng']
-env['LIBS'] += env.StaticLibrary('png', files)