Remove use of `ovarrf()` and `ocosts()`

[clmould]

Uses of ovarrf and ocosts could not be remove in #4405 as they are used by other packages. When possible, these should be removed from PROCESS

[timothy-nunn]

@j-a-foster can you please move cost model 3 over to using ovarre from ovarrf (they have the same arguments, its just a case of find and replace). After that, you can delete the function ovarrf.

ocosts is a little more involved because the order of arguments is different. Again, once you move everything in PROCESS/cost model 3 to use ovarre (remember to re-order the arguments when calling!) you can delete the function ocosts.