Switch back GitHub Actions workflow to use current Tycho version

The Tycho version used in GitHub Actions workflow has been temporarily
reverted to 4.0.8. This change switched back the Tycho version defined
in the Tycho build itself.

Author: HeikoKlare

.github/workflows/maven.yml

@@ -71,7 +71,6 @@ jobs:
         --fail-at-end
         -DskipNativeTests=false
         -DfailIfNoTests=false
-        '-Dtycho.version=4.0.8'
         clean install
     - name: Performance tests
       if: contains(github.event.pull_request.labels.*.name, 'performance')