Charge transfer coefficients defined but not use.

[brosaplanella]

Issue

In most parameter sets we define "Positive/Negative electrode charge transfer coefficient", which is set to 0.5. This parameter actually is not used anywhere, which is confusing. The actual parameter used in AsymmetricButlerVolmer is "Positive/Negative electrode Butler-Volmer transfer coefficient", but as far as I can tell AsymmetricButlerVolmer is not used in any of the models.

Proposed solution

Short term:

• Remove the "Positive/Negative electrode charge transfer coefficient" from all parameter sets.

Longer term (needs discussion/separate issue):

• Make AsymmetricButlerVolmer the default with the (right) charge transfer coefficient defined as 0.5 in the parameter sets (behaviour should be the same as we have now, not sure how performance will be affected).

[Daniel-Nicolae23]

Just a heads-up that AsymmetricButlerVolmer becoming the default would be a breaking change. There is no corresponding inverse kinetics submodel, so any code using "surface form": "false" would break, unless the users switch back to "intercalation kinetics": "symmetric Butler-Volmer" explicitly.