IO diagnostic structure in the code but not ~~used at all~~ half used

[hkershaw-brown]

• diagnostic structure in the code but not used at all half used?

  DART/assimilation_code/modules/io/state_structure_mod.f90

  Lines 131 to 135 in 924182f

  	! diagnostic files
  	!>@todo FIXME these routines are deprecated because we are no supporting 'diagnostic'
  	!> files, but they will likely be useful for the single file (multiple member) input.
  	public :: create_diagnostic_structure, &
  	end_diagnostic_structure

Note this routines comment says is is depreciated

DART/assimilation_code/modules/io/state_structure_mod.f90

Lines 131 to 135 in f193ab4

	! diagnostic files
	!>@todo FIXME these routines are deprecated because we are no supporting 'diagnostic'
	!> files, but they will likely be useful for the single file (multiple member) input.
	public :: create_diagnostic_structure, &
	end_diagnostic_structure

Then Used with a comment "may not be needed"

Then domain = 1 is hardcoded anyway

DART/assimilation_code/modules/io/direct_netcdf_mod.f90

Lines 2266 to 2273 in f193ab4

	! may not be needed
	ncFileID%diag_id = create_diagnostic_structure()
	my_ncid = ncFileID%ncid
	!>@todo ONLY ONE DOMAIN FOR SINGLE FILE OUTPUT
	domain = 1
	do ivar = 1, get_num_variables(domain)

Originally posted by @hkershaw-brown in #359