clean up aerosol-related fields in met_force_type??

[gmao-rreichle]

The implementation of the dirty snow albedo (GOSWIM) in GEOSldas introduced 60 new forcing fields in met_force_type (DUDP001, DUDP002, etc).
It is unclear if the implementation works at this time. Chances are it does not because there's not a corresponding MPI type in LDAS_ensdrv_mpi.F90.
Also, the aerosol forcing fields are not considered in subroutine check_nodata_forcing().
It is unclear how much unneeded memory is allocated, and whether clean-up might be needed to free up this memory.
I am writing this up now because I noticed these issues during my recent clean-up of the met forcing code and wanted to make a note somewhere. No immediate action is necessary.
@weiyuan-jiang @biljanaorescanin