Remove unused code for function segments.

 To be re-introduced later, as needed.

 * docs/cfgobjects.rst: Remove CfgFunctionSegment.
 * pyrseas/augment/function.py (CfgFunctionSegment): Removed class.
   (CfgFunctionSourceDict.__init__): Remove cfg_segments argument.
   (CfgFunction.adjust_name): Remove as unused.  (CfgFunction.apply):
   Remove processing of segments.
 * pyrseas/augmentdb.py (AugmentDatabase.__init__): Remove segments
   parameter in initialization of CfgFunctionSourceDict.