[BYOC] Remove ext params stored in metadata from params to avoid duplication

[trevor-m]

This PR is an alternative to #7564

During compilation, weights from external modules are stored in the MetadataModule (.so), but they are still kept in params so they end up being duplicated.

This PR will remove from params only the weights which were stored in MetadataModule, solving the weight duplication issue.

[trevor-m]

@comaniac @zhiics @mbaret @d-smirnov

[comaniac]

The change looks clean and good to me. Could you add a test case?

[trevor-m]

Thanks @comaniac
I added an assert to an existing test.
Without this pr, the assert fails:

        # Params will be stored in metadata module.
>       assert len(graph_module.get_params()) == 0
E       AssertionError: assert 1 == 0
E        +  where 1 = len({'ccompiler_0_const_0': <tvm.nd.NDArray shape=(1,), cpu(0)>\narray([1.], dtype=float32)})
E        +    where {'ccompiler_0_const_0': <tvm.nd.NDArray shape=(1,), cpu(0)>\narray([1.], dtype=float32)} = <bound method GraphExecutorFactoryModule.get_params of <tvm.relay.backend.graph_executor_factory.GraphExecutorFactoryModule object at 0x7fd7e2831dd8>>()
E        +      where <bound method GraphExecutorFactoryModule.get_params of <tvm.relay.backend.graph_executor_factory.GraphExecutorFactoryModule object at 0x7fd7e2831dd8>> = <tvm.relay.backend.graph_executor_factory.GraphExecutorFactoryModule object at 0x7fd7e2831dd8>.get_params

[comaniac]

LGTM

[comaniac]

Thanks @trevor-m