[opti] Unannotate sections in-place

This avoids unecessary copies. This is a preparatory step to
reimplementing the extends algorithm. It may be that this breaks
the extends algorithm as it is currently implemented.

src/zc/buildout/buildout.py

@@ -261,11 +261,14 @@ def _print_annotate(data, verbose, chosen_sections, basedir):
 
 
 def _unannotate_section(section):
-    return {key: entry.value for key, entry in section.items()}
-
+    for key in section:
+        section[key] = section[key].value
+    return section
 
 def _unannotate(data):
-    return {key: _unannotate_section(section) for key, section in data.items()}
+    for key in data:
+        _unannotate_section(data[key])
+    return data
 
 
 def _format_picked_versions(picked_versions, required_by):
@@ -1593,7 +1596,7 @@ class Options(DictMixin):
             result = _annotate_section(result, "")
             data = _annotate_section(copy.deepcopy(data), "")
             _update_section(result, data)
-            result = _unannotate_section(result)
+            _unannotate_section(result)
             result.pop('<', None)
             return result
         finally: