'rotations' parameter is redundant if Qrack converts to observable basis

[WrathfulSpatula]

expval() has a parameter for the observable type to calculate, but this turns out to be redundant with rotations parameter passed into apply_operations(): I realize now, one either uses rotations parameter or transforms basis for expval() parameters, not both.

[cosenal]

LGTM
(details discussed on Discord)

[WrathfulSpatula]

For everyone else's sake: @cosenal noted that the wrapper method, without parsing rotations, was redundant if rotations wasn't used. I removed the level of indirection, but I kept the (public API method) signature, as it seems to be what PennyLane expects (since it does pass in rotations as a kwarg).