[FIRRTL] Drop unused imports in LayerSink, NFC

Drop some unused imports that my LSP is telling me can be dropped.

Signed-off-by: Schuyler Eldridge <[email protected]>

Author: seldridge

lib/Dialect/FIRRTL/Transforms/LayerSink.cpp

@@ -12,14 +12,11 @@
 
 #include "circt/Dialect/FIRRTL/FIRRTLInstanceGraph.h"
 #include "circt/Dialect/FIRRTL/FIRRTLOps.h"
-#include "circt/Dialect/FIRRTL/Passes.h"
 #include "circt/Support/Debug.h"
 #include "mlir/IR/Dominance.h"
 #include "mlir/IR/Threading.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
-#include "mlir/Pass/Pass.h"
 #include "mlir/Transforms/ControlFlowSinkUtils.h"
-#include "llvm/ADT/PostOrderIterator.h"
 
 #define DEBUG_TYPE "firrtl-layer-sink"