Remove shadow artifact for `diktat-runner`

`diktat-runner:shadow` was added for spotless.
But Gradle and Maven use different notations for maven coordinate:
- gradle: `com.saveourtool.diktat:diktat-runner:<version>:shadow`
- maven `com.saveourtool.diktat:diktat-runner:jar:shadow:<version>`

Since Spotless has a common code base for both plugins we can't use the shadow plugin. But the regular dependency should work fine