OscConfigParser.py: fix __delitem__

Two issues:
- There is no _find() member in ConfigLineOrder. Use _find_section()
  instead
- Use 'key' instead of 'line' as argument for _find_section() since
  'line' is used before assignment.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>

osc/OscConfigParser.py

@@ -74,7 +74,7 @@ def __getitem__(self, key):
         return section
 
     def __delitem__(self, key):
-        line = self._find(line)
+        line = self._find_section(key)
         if not line:
             raise KeyError(key)
         self._lines.remove(line)