Remove references to mcoe

[bendnorman]

The table formerly known as mcoe never actually contained marginal cost of electricity information, just some derived generator attributes that don't include financial information. #2904 adds all generator attributes to the old mcoe and renamed to out_eia__yearly_generators and out_eia__monthly_generators so it's clear they are the primary tables users should interact with if they are interested in EIA generator information. The PR only renames the assets and tables but does not rename references to mcoe in the code.

Tasks

Beta Give feedback

1. Rename modules
2. Variables
3. references in doc strings
4. references in tests

[zaneselvans]

Well, we have one component of MCOE... fuel costs per MWh. But none of the non-fuel fixed & variaible operating costs or capital investments. So a pretty incomplete picture.