re-running the OAAT ensemble

[linniahawkins]

A new nitrogen fixation temperature equation has been added to CLM6 ESCOMP/CTSM#2869. This has substantial implications for other processes and likely influences survivability and range tests. We have decided to re-run the OAAT.

• Since we are not using Houlton et al., thus we will exclude the a_fix parameter.
• We will add and test three new parameters from the new Nfix function to the OAAT for testing.

[linniahawkins]

In addition, we will add parameters from the new Meier et al., roughness scheme, which were previously hardcoded.