Cleanup: Fix build warnings from OSL shader compilation

There were to copies of stdosl.h one from stock OSL
and one in the cycles tree augmented with cycles
specific closures.

moved the cycles ones to stdcycles.h and copied
the stock stdosl.h and accompanying headers from
the OSL shader folder.

for further details see D6812.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D6812

intern/cycles/kernel/shaders/node_convert_from_point.osl

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include "stdosl.h"
+#include "stdcycles.h"
 
 shader node_convert_from_point(point value_point = point(0.0, 0.0, 0.0),
                                output string value_string = "",