Cycles:
* Revert r57203 (len() renaming)
There seems to be a problem with nVidia OpenCL after this and I haven't figured out the real cause yet. 
Better to selectively enable native length() later, after figuring out what's wrong. 

This fixes [#35612].

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57235 954f8c5b-7b00-dc11-b283-0030488c597c