[sextante] update sample script to new API (fix #8278)

Author: alexbruy

python/plugins/sextante/script/scripts/Split_vector_layer_by_attribute.py

@@ -15,8 +15,6 @@
 # We get the actual object,
 layer = sextante.getobject(input)
 provider = layer.dataProvider()
-allAttrs = provider.attributeIndexes()
-provider.select( allAttrs )
 fields = provider.fields()
 writers = {}
 
@@ -44,6 +42,5 @@
     outFeat.setAttributes(atMap)
     writers[clazz].addFeature(outFeat)
 
-
 for writer in writers.values():
-    del writer
+    del writer