If you delete a a package, there are various problems/inconsistencies that may come up.
1. If you have subpackages, they won't get deleted. eg. adobe core components package
2. If you have bundles, they won't get deleted.
So ideally you should include the uninstall the package. This step as the first step in your deployment process.
1. if you have a blue green deployment strategy, you can uninstall until the latest version.
2. If not, you can think of the below process with a rule to uninstall until n-1 version.
For uninstall, there is no straight away API to consume, but the best way is
1. Fetch the list of packages /crx/packmgr/list.jsp using curl
2. Parse the results with any identifier like package name in the pipeline
3. Invoke uninstall using curl like curl -u admin:admin -F cmd=uninstall http://localhost:4502/crx/packmgr/service/.json/etc/packages/my_packages/test.zip
A ruby gem reference which can outline the delete process(not uninstall process) is available at [1] and a brilliant article on the whole deployment strategy is at [2].
[1] - https://github.com/vrtdev/aemcrxpkgmgr/blob/d62c151ee6a6858ce1d769f8ae9a0696ff040a7c/lib/aemcrxpkgmgr.rb
[2] - https://medium.com/vrt-digital-studio/13-steps-to-rock-stable-aem-package-installs-d9bbba1f7b15
Thanks,
Nirmal Jose