Revert deprecation warning fix

@imyhxy it seems we can't apply the deprecation warning fix because then export fails, so I'm reverting my previous change here.

export.py

@@ -307,7 +307,7 @@ def export_engine(model, im, file, train, half, simplify, workspace=4, verbose=F
  LOGGER.info(f'{prefix} building FP{16 if half else 32} engine in {f}')
  if half:
  config.set_flag(trt.BuilderFlag.FP16)
- with builder.build_serialized_network(network, config) as engine, open(f, 'wb') as t:
+ with builder.build_engine(network, config) as engine, open(f, 'wb') as t:
  t.write(engine.serialize())
  LOGGER.info(f'{prefix} export success, saved as {f} ({file_size(f):.1f} MB)')