Remove PR template in favor of org-wide community health template (#7792)

## Rationale

Removes this repo's local `.github/pull_request_template.md` in favor of
an organization-wide community health PR template. GitHub falls back to
the org-level default template (defined in the `.github` repo) for any
repo that does not define its own, so deleting the per-repo template
lets every LabKey repo share one consistent template maintained in a
single place.

## Related Pull Requests

- LabKey/limsModules#2299

## Changes

- Deleted `.github/pull_request_template.md`; the org-wide community
health template now applies.

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Co-authored-by: Lum <[email protected]>

Author: labkey-martyp