rocr: remove unused agent properties reference in scratch initialization

The agent properties variable `agent_props` was declared but never used
in the `InitScratchSRD()` function. Which casued compile warning:

runtime/core/runtime/amd_aql_queue.cpp:1880:15: warning:
unused variable ‘agent_props’ [-Wunused-variable]
 1880 |   const auto& agent_props = agent_->properties();

No functional changes, purely a code cleanup commit.

runtime/hsa-runtime/core/runtime/amd_aql_queue.cpp

@@ -1877,8 +1877,6 @@ void AqlQueue::InitScratchSRD() {
   amd_queue_.scratch_backing_memory_location = queue_scratch_.main_queue_process_offset;
   amd_queue_.alt_scratch_backing_memory_location = queue_scratch_.alt_queue_process_offset;
 
-  const auto& agent_props = agent_->properties();
-
   // For backwards compatibility this field records the per-lane scratch
   // for a 64 lane wavefront. If scratch was allocated for 32 lane waves
   // then the effective size for a 64 lane wave is halved.