Revert package-ecosystem
Revert package-ecosystem

The configuration docs are confusing:

> Note: Dependabot also supports the following package managers:
> ...
> - `pipenv`, `pip-compile`, and `poetry` (specify `pip`)

https://docs.github.com/en/free-pro-team@latest/github/administering-a-repository/configuration-options-for-dependency-updates#package-ecosystem

However, `pip-compile` resulted in an error:

Dependabot encountered the following error when parsing your .github/dependabot.yml:
```
The property '#/updates/0/package-ecosystem' value "pip-compile" did not match one of the following values: npm, bundler, composer, maven, mix, cargo, gradle, nuget, gomod, docker, elm, gitsubmodule, github-actions, pip, terraform
```

dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq