Deprecate PauliTransform?

[BichengYing]

Under the ops.clifford_gate, there is a data structure PauliTransform, which is just a named tuple

PauliTransform = NamedTuple('PauliTransform', [('to', Pauli), ('flip', bool)])
document(PauliTransform, """+X, -X, +Y, -Y, +Z, or -Z.""")

The reason I suggest deprecation is

1. It is only used in SingleQubitCliffordGate.
2. For multiple qubits Clifford gate, this named structure doesn't fit.
3. We have a replacement now -- DensePauliString.
4. The stabilizers and destabilizers of Clifford Tableau return as DensePauliString anyway.

The benefit of keeping PauliTransform is it is much more light-weighted than DensePauliString. But I think the benefits is marginal.

[Strilanc]

Agreed, should deprecate because obsoleted by DensePauliString and not widely used.

[MichaelBroughton]

@ybc1991 can we close this ?

[dabacon]

@MichaelBroughton I think this still exists. This is one to deprecate before 0.15?