Remove cross-version suffix from artifactIds

[fthomas]

This makes it easier to compare them with updates of created
PRs which are already persisted without cross-version suffix.

[codecov]

Codecov Report

Merging #493 into master will decrease coverage by 0.23%.
The diff coverage is 12.5%.

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
- Coverage   56.75%   56.51%   -0.24%     
==========================================
  Files          64       64              
  Lines         770      775       +5     
  Branches       32       31       -1     
==========================================
+ Hits          437      438       +1     
- Misses        333      337       +4

Impacted Files	Coverage Δ
...a/org/scalasteward/core/update/UpdateService.scala	0% <0%> (ø)	⬆️
.../main/scala/org/scalasteward/core/sbt/SbtAlg.scala	54.05% <0%> (-6.56%)	⬇️
...ain/scala/org/scalasteward/core/model/Update.scala	100% <100%> (ø)	⬆️

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