Remove hh5 references

[marc-white]

Blocks #230 .

With CLEX closing in December, anything on hh5 will no longer be maintained. All data & documentation references/dependencies on hh5 need to be removed.

[marc-white]

This appears to be stuck behind ACCESS-NRI/ACCESS-Analysis-Conda#123 .

In attempting to update the outputs of usage/quickstart.ipynb, the lack of package nc-time-axis in access-med causes an error at cell 23.

[marc-white]

See issues starting at: #230 (comment)