Clean up covariate

[ValentineHerr]

Here is a list of variables and covaritates associations that should not exist in ForC. It needs to be cleaned up.

variable.name	covariate_1	notes
biomass_ag	max.diameter	0 (surprised we have that)
ANPP_woody_branch	max.diameter_branch	0 (surprised we have that)
ANPP_litterfall_2	max.diameter_branch	0 (surprised we have that)
biomass_ag	max.diameter_root	0 (surprised we have that)
biomass_ag	max.diameter_twig	0 (surprised we have that)
biomass_root	min.depth	0 (surprised we have that--should always be 0)
biomass_ag_woody	min.diameter_root	database error-- should not exist
biomass_ag_foliage	min.diameter_root	database error-- should not exist
biomass_ag_foliage	min.length	0 (surprised we have that)
biomass_ag	min.length	0 (surprised we have that)
organic.layer	min.length	0 (surprised we have that)
woody.mortality_ag	NA	? - 0 (but should include min.DBH)

variable.name	covariate_2	notes
deadwood_down	max.diameter	0 (surprised we have that)
biomass_root	max.diameter	? (probably not needed- I'm surprised that's reported)
biomass_root_coarse	max.diameter_root	? (probably not needed- I'm surprised that's reported)