ARMI should not forcibly add a SFP to the Reactor

[john-science]

Right now, ARMI forcibly adds a Spent Fuel Pool (SFP) to every Reactor object:

armi/armi/reactor/reactors.py

Lines 213 to 214 in 5a41b25

	if not any(structure.typ == "sfp" for structure in bp.systemDesigns.values()):
	bp.addDefaultSFP()

I think this is rather a lazy idea and default, meant to temporarily help out a small number of users downstream who had blueprints that didn't have SFPs in them.

I think it's time to pull the Band-Aid™ off, and make people define their own SFP in the blueprints.

And, not for nothing, I just hate the default values that are in our default SFP:

armi/armi/reactor/blueprints/__init__.py

Line 558 in 5a41b25

def addDefaultSFP(self):

armi/armi/reactor/assemblyLists.py

Lines 108 to 110 in 5a41b25

	self.spatialGrid = grids.CartesianGrid.fromRectangle(50.0, 50.0)
	self._filler = RowMajorAutoFiller(self, 10)