[WIP] Move hillslope variables off surface dataset

[samsrabin]

Work in progress! Do not review!

Subject to force pushes!

Description of changes

This PR moves the variables required for hillslope runs off the surface dataset and onto the new hillslope_file. This makes it so we don't have to maintain a hillslope-specific surface dataset for testing purposes. If/when running with hillslopes becomes the default, we can move these variables back onto the surface dataset.

Specific notes

Contributors other than yourself, if any: None

CTSM Issues Fixed (include github issue #): None

Are answers expected to change (and if so in what way)? No

Any User Interface Changes (namelist or namelist defaults changes)? No

Testing performed, if any:

• Derecho hillslope tests are b4b-identical with ctsm5.1.dev174
• Izumi hillslope tests are b4b-identical with ctsm5.1.dev174
• Other Derecho and Izumi aux_clm tests are b4b-identical with ctsm5.1.dev174

Remaining work

• Merge in 5.2 tag
• Update surface dataset specified in Hillslope testmod: Use default 10x15 fsurdat
• Update synthetic hillslope dataset specified in Hillslope testmod, if needed

[samsrabin]

Blocked: Waiting on 5.2.

[samsrabin]

5.2 is in, so this is no longer blocked.