Fix compilation with newer flatbuffers (#17164)
In flatbuffers@v23.5.9 was broken forward declaration for
FlatBufferBuilder. Trying to compile onnxruntime falls with the
following error:
```
flatbuffers/include/flatbuffers/flatbuffer_builder.h:1420:38: error: typedef redefinition with different types ('FlatBufferBuilderImpl<false>' vs 'flatbuffers::FlatBufferBuilder')
typedef FlatBufferBuilderImpl<false> FlatBufferBuilder;
^
onnx_runtime/include/onnxruntime/core/graph/graph.h:47:11: note: previous definition is here
class FlatBufferBuilder;
```
This PR removes these declarations and puts includes instead
