Removing tracers in variable list that have been turned off by default

[darincomeau]

Removes two variables, iceAge and firstYearIceArea, from the list of validated variables in the seaice exact restart test. These tracers have recently been turned off by default in E3SM for v3 (E3SM-Project/E3SM#6090).

Checklist

• Testing comment in the PR documents testing used to verify the changes

With this branch:

Test Runtimes:
00:09 PASS seaice/single_column/standard_physics
00:02 PASS seaice/single_column/exact_restart
Total runtime 00:11
PASS: All passed successfully!

Addresses #159 (already closed).

[xylar]

@darincomeau, sorry for the slow response. I'm approving by inspection and based on your testing.