Remove hardware argument in qml.qinfo.quantum_fisher

[Qottmann]

Following the suggestions given in #2684, removed the hardware argument and adapted the doc-string.

I noticed that something like this will not work then, but I am assuming this is expected behavior for passing a qnode instead of a qfunc to qml.QNode:

dev = qml.device("default.qubit", wires=1)

@qml.qnode(dev)
def circ(params):
    qml.RY(params[0], wires=1)
    return qml.expval(qml.PauliX(0))

dev_finite = qml.device("default.qubit", wires=1, shots=1000)

circ = qml.QNode(circ, dev_finite)

>>> print(circ.device.shots)
None

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[josh146]

Thanks @Qottmann! Just a few minor changes, and one larger change. I think the reason that adjoint_metric_tensor requires default.qubit is because it requires knowledge of how to apply statevectors within a device, so it is making use of the internal default.qubit api 🤔

Note that, since lightning.qubit inherits from default.qubit, the adjoint method works here as well :)

>>> from pennylane.devices import DefaultQubit
>>> dev = qml.device("lightning.qubit", wires=3)
>>> isinstance(dev, DefaultQubit)
True