Cycles: Replace __MAX_CLOSURE__ build option with runtime integrator variable

Goal is to reduce OpenCL kernel recompilations.

Currently viewport renders are still set to use 64 closures as this seems to
be faster and we don't want to cause a performance regression there. Needs
to be investigated.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D2775

intern/cycles/device/device_split_kernel.cpp

@@ -34,7 +34,6 @@ DeviceSplitKernel::DeviceSplitKernel(Device *device)
   use_queues_flag(device, "use_queues_flag"),
   work_pool_wgs(device, "work_pool_wgs")
 {
-	current_max_closure = -1;
 	first_tile = true;
 
 	avg_time_per_sample = 0.0;
@@ -116,8 +115,6 @@ bool DeviceSplitKernel::load_kernels(const DeviceRequestedFeatures& requested_fe
 
 #undef LOAD_KERNEL
 
-	current_max_closure = requested_features.max_closure;
-
 	return true;
 }