Removed functionality from MPAS framework that overwrites attributes

[akturner]

Removed functionality from MPAS framework that overwrites Registry attributes with stream file attributes. This change prevents input files from overwriting CF-compliant units in Registry with non-CF compliant ones in the input file.

Fixes #4986

[BFB]

[xylar]

@akturner, thank s a lot for making this PR. I'd like to test it with some other CF changes from the Hackathon, which I'm still working on. It would be good to test with @darincomeau's units changes, too.

[rljacob]

@xylar how are those tests going?

[xylar]

@rljacob, it's not. I have too much else on my plate at the moment.

[xylar]

@akturner, sorry for the delay. I tested this with standalone MPAS-Ocean in compass (in a test E3SM branch where I also merged #5026 and #5027), and it worked like a charm! I used an initial condition from before, where the units for salinity are:

	double salinity(Time, nCells, nVertLevels) ;
		salinity:long_name = "salinity" ;
		salinity:units = "grams salt per kilogram seawater" ;

The resulting output is:

	double salinity(Time, nCells, nVertLevels) ;
		salinity:long_name = "salinity grams salt per kilogram seawater"
 ;
		salinity:units = "1.e-3" ;

as desired.

In time series stats daily, I also see:

	double timeDaily_avg_activeTracers_salinity(Time, nCells, nVertLevels) ;
		timeDaily_avg_activeTracers_salinity:long_name = "salinity grams salt per kilogram seawater" ;
		timeDaily_avg_activeTracers_salinity:units = "1.e-3" ;

[xylar]

@mark-petersen and @matthewhoffman, please give this a try as well when you can.

[mark-petersen]

I agree, this works as expected based on @xylar's test above. Thanks.

[matthewhoffman]

I'm approving by inspection and the testing that Xylar and Mark did. This is a valuable change.

[jonbob]

passes sanity testing, merged to next

[jonbob]

merged to master