fix: rm short-circuit in rc.unraid-api if plugin config dir is absent (#1515)

This short-circuit causes any/all `rc.unraid-api` invocations to
immediately fail on fresh 7.2 images (because
`/boot/config/dynamix.my.servers` doesn't exist).

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Refactor**
* Removed initial checks and setup for a plugin directory and default
environment file in the startup script.
* Simplified environment switching with streamlined commands and
improved error handling.
* Removed deprecated environment path references and updated related
tests.
* **Documentation**
* Added descriptive comments clarifying build and environment settings.
* **Tests**
* Updated test cases by removing assertions related to deprecated
environment paths.
* **Maintenance**
  * Updated timestamp fixtures for consistency.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

plugin/source/dynamix.unraid.net/etc/rc.d/rc.unraid-api

@@ -4,9 +4,6 @@
 # shellcheck source=/dev/null
 source /etc/profile
 
-flash="/boot/config/plugins/dynamix.my.servers"
-[[ ! -d "${flash}" ]] && echo "Please reinstall the Unraid Connect plugin" && exit 1
-[[ ! -f "${flash}/env" ]] && echo 'env=production' >"${flash}/env"
 unraid_binary_path="/usr/local/bin/unraid-api"
 api_base_dir="/usr/local/unraid-api"
 scripts_dir="/usr/local/share/dynamix.unraid.net/scripts"