#2696: correct the doco that ST_NumInteriorRings no longer works with multipolygons since polys, also get rid of synonym description. People can just look back at main function name.

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@12414 b70326c6-7e19-0410-871a-916f4a2858ee