remove Strang + MOL (time_integration_method = 1)

[zingale]

The new SDC method is merged and does proper coupling of hydro and reactions, making the Strang + MOL method not necessary. If we want to do Strang, then CTU is better. If we want to do a MOL-style integration, then the SDC integration, even 2nd order in time, should be better than the MOL. Furthermore, the SDC method extends more easily to AMR + subcycling.

I propose we remove the pure MOL (RK time integration) method, since we are not likely to use it and don't want to support it.