Remove includesls macro definition and usage as not relevant

[vzhestkov]

What does this PR change?

There is no need to define and use distinct macro for just a simple task to include SLS.
So removing it.

GUI diff

No difference.

Documentation

• No documentation needed: only internal and user invisible changes

Test coverage

• No tests: no proper tests for this part, highstate apply will fail for the client if the state is wrong

Changelogs

Make sure the changelogs entries you are adding are compliant with https://github.com/uyuni-project/uyuni/wiki/Contributing#changelogs and https://github.com/uyuni-project/uyuni/wiki/Contributing#uyuni-projectuyuni-repository

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• Re-run test "changelog_test"
• Re-run test "backend_unittests_pgsql"
• Re-run test "java_pgsql_tests"
• Re-run test "schema_migration_test_pgsql"
• Re-run test "susemanager_unittests"
• Re-run test "javascript_lint"
• Re-run test "spacecmd_unittests"

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[raulillo82]

LGTM. Tested with openEueler.