[dynamo] Revert C++-fying of symbolic shape guards

Moving symbolic shape guards to C++ causes compile time issues. This
basically boils down to a tradeoff question.

For models that have large amount of dynamic shape guards, this flag
will help reduce guard latency. But for most of the models, that have a
very few dynamic shape guards, the guard lantecy is anyways small. These
models will still see a high compile time hit because of calling gcc
during the compile.

So a good default value seems to be False. We can write a doc to give
guidance on reducing guard latency.

torch/_dynamo/config.py

@@ -445,7 +445,7 @@ use_numpy_random_stream = False
 enable_cpp_guard_manager = True
 
 # Use C++ guard manager for symbolic shapes
-enable_cpp_symbolic_shape_guards = not is_fbcode()
+enable_cpp_symbolic_shape_guards = False
 
 # Enable tracing through contextlib.contextmanager
 enable_trace_contextlib = True