Make saltenv stripping more concise

We're already filtering __pub_* arguments from the kwargs before using
them to write the key/value pairs in repo config files, no need to do
two extra dict lookups here. This commit excludes saltenv from the repo
args in the same list comprehension where __pub_* arguments are
filtered.
Merge pull request #12901 from terminalmage/clean-saltenv

Make saltenv stripping more concise