Merge #329

329: remove soil plant hydrology example r=kmdeck a=kmdeck

## Purpose 
We are not actively using the soil-plant hydrology only example. It is useful primarily for debugging but we havent used it in a while. the realism is quite limited (prescribed evaporation, for example) so we dont think it will be that useful.


## To-do


## Content
Removes the soil_plant_hydrology_model.jl
Moves the root_flux_per_ground_area and the RootExtraction source definitions to soil_canopy_model.jl (previously, both soil+plant models used the same methods and those were defined in soil_plant_hydrology_model.jl)
Removes the experiment from buildkite which runs the simulation.


Review checklist

I have:
- followed the codebase contribution guide: https://clima.github.io/ClimateMachine.jl/latest/Contributing/
- followed the style guide: https://clima.github.io/ClimateMachine.jl/latest/DevDocs/CodeStyle/
- followed the documentation policy: https://github.com/CliMA/policies/wiki/Documentation-Policy
- checked that this PR does not duplicate an open PR.

In the Content, I have included 
- relevant unit tests, and integration tests, 
- appropriate docstrings on all functions, structs, and modules, and included relevant documentation.

----
- [X] I have read and checked the items on the review checklist.


Co-authored-by: kmdeck <kdeck@caltech.edu>

.buildkite/pipeline.yml

@@ -40,10 +40,6 @@ steps:
         command: "julia --color=yes --project=experiments experiments/standalone/Soil/evaporation.jl"
         artifact_paths: "experiments/standalone/Soil/evaporation*png"
 
-      - label: "ozark_test_hydrology_only"
-        command: "julia --color=yes --project=experiments experiments/integrated/ozark/hydrology_only/ozark.jl"
-        artifact_paths: "experiments/integrated/ozark/hydrology_only/*png"
-
       - label: "ozark_test"
         command: "julia --color=yes --project=experiments experiments/integrated/ozark/ozark.jl"
         artifact_paths: "experiments/integrated/ozark/*png"