[LTM] Reverse redefinition of farmland terrain as plains

[zijistark]

I'm assigning this to @DelnarErsike and myself, because @Leybrook (kotten) is not yet assignable due to not being on EMFTeam.

I quote from Slack:

@Leybrook

Due to the expansion of farmland, I needed it to be visual rather than affect the game mechanics too much, so I redefined farmland to work as plains
the only difference between plains and farmland is "max_attrition = -0.01" being added on the latter
and the provinces would get less attrition as they develop naturally anyhow
so this was the tradeoff for visual expansion (edited)
italian provinces get farmland due to history files

@DelnarErsike

Re: the differences, traits can add affinity for one but not the other, and events and effects can trigger off of one terrain type but not the other (e.g. in the current EMF beta, farmlands give less > Nomad population per empty holding than plains because the suitability between sedentary and nomadic lifestyles is much more in sedentary's favor in farmlands than they are in plains).
But my main concern here is actually the interaction between visuals and mechanics. CK2 doesn't have a simple terrain map mode, so seeing farmland-like terrain graphics can more easily lead people to > believe that the province is a farmland one (at a glance).
Which is true for cases like provinces in Italy and Denmark (because SWMH has manually set province terrain types to farmland there), but not for ones in East Anglia or Normandy.

@Leybrook

Ill change it then.