REBCO critical current adjustment for type of cable

[chris-ashe]

For the hijc_rebco function in superconductors.py that calculates the critical current of the REBCO tape there is a fudge factor at the end of the function.

jcrit = (
        jcrit
        * (rebco_variables.tape_width * rebco_variables.rebco_thickness)
        / (rebco_variables.tape_width * rebco_variables.tape_thickness)
        * 0.4
    )

The 0.4 factor was introduced to scale the critical current under the assumption of using CORC style cables.
https://www.advancedconductor.com/corccable/

This is not in-line with what PROCESS assumes for the turn structure as a rectangular tape block is assumed.