Update HMIS test date usage, remove TIME_FMT

[gigxz]

Merging this PR

• use the squash-merge strategy for PRs targeting a release-X branch
• use a merge-commit or rebase strategy for PRs targeting the stable branch

Description

• Remove the TIME_FMT thing because there were warnings about repeated declarations and we don't need it
• Update some tests to use the pattern of setting today/yesterday as vars to use throughout the test, so they are more robust to running near midnight

Type of change

Cleanup

Checklist before requesting review

• I have performed a self-review of my code
• I have run the code that is being changed under ideal conditions, and it doesn't fail
• If adding a new endpoint / exposing data in a new way, I have:
  • ensured the API can't leak data from other data sources
  • ensured this does not introduce N+1s
  • ensured permissions and visibility checks are performed in the right places
• I have updated the documentation (or not applicable)
• I have added spec tests (or not applicable)
• I have provided testing instructions in this PR or the related issue (or not applicable)

[martha]

Nice, thank you

[ttoomey]

Looks good! Thanks for making the assessment test more reliable