Influence of Unused Transient on the Signature

As far as I can tell the recent [fix to `LoopToMap`](https://github.com/spcl/dace/pull/2349) introduced a change in behaviour.
The PR also modified how `SDFG::_used_symbols_internal()` works and in my opinion changed it in a non desirable way.

Consider the following script:
```python=
import dace
import pytest

def _make_sdfg_with_unused_transient(create_unused_transient: bool) -> dace.SDFG:
sdfg = dace.SDFG("unused_transient")
state = sdfg.add_state()

for name in "ab":
sdfg.add_array(
name,
shape=(10,),
dtype=dace.float64,
transient=False,
)

sdfg.add_symbol("x_shape", dace.int32)
if create_unused_transient:
sdfg.add_array(
"x",
shape=("x_shape",),
dtype=dace.float32,
transient=True,
)

state.add_mapped_tasklet(
"map",
map_ranges={"__i": "0:10"},
inputs={"__in": dace.Memlet("a[__i]")},
code="__out = __in + 1.90",
outputs={"__out": dace.Memlet("b[__i]")},
external_edges=True,
)

return sdfg

if __name__ == "__main__":
create_unused_transient = True
sdfg: dace.SDFG = _make_sdfg_with_unused_transient(create_unused_transient)

print(f"Free Symbols: {sdfg.free_symbols}")
print(f"arglist(): {sdfg.arglist()}")
print(f"signature_arglist(): {sdfg.signature_arglist()}")
print(f"signature_init_arglist(): {sdfg.init_signature()}")
```

As you can see depending on `create_unused_transient` the SDFG may or may not contain data descriptor with name `x`, that when it is present is not used.
Furthermore, the array has a symbolic size of `x_shape`, that symbol, however, is always present.
If you run that script using DaCe `2.0.0a3`, then `x_shape` will _not_ be part of the signature.

But if you use current `main` (`a6717b608f497190205d`) then `x_shape` will part of the signature if `create_unused_transient` is `True`.
However, if `create_unused_transient` is `False` then it will not be present.
It is important to notice that even if `x_shape` is present in the signature it is not used, i.e. the array is not allocated.

My question now is what is the correct behaviour?
In my opinion `x_shape` should not be part of the signature and this is an unintended side effect.