Deprecate number of electrodes in parallel to make a cell

[aabills]

The "Number of electrodes connected in parallel to make a cell" parameter is confusing and not always used properly. For example, it is not used to calculate the area of the current collector:

PyBaMM/src/pybamm/parameters/geometric_parameters.py

Line 44 in 7419219

self.A_cc = self.L_y * self.L_z # Current collector cross sectional area

, which is used to calculate the "total lithium in the electrolyte":

PyBaMM/src/pybamm/parameters/lithium_ion_parameters.py

Line 116 in 7419219

self.n_Li_e_init = c_e_av_init * self.L_x * self.A_cc

We could go through and try and find and fix all of these, or we could just deprecate this parameter. I think we should do the latter.