Drop custom verification-metadata workflow; Renovate maintains it

Verified empirically on a live Mend-hosted fork: when its PR branch is not
externally modified, Renovate runs ./gradlew --write-verification-metadata
and commits the refreshed gradle/verification-metadata.xml itself (jetty-http
10.0.0: jar+pom+parent checksums authored by renovate[bot], no workflow
present). The custom workflow only appeared necessary because its commit
raced Renovate's on push; removing it lets Renovate self-maintain.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Jon Bartels <jonathan.bartels@gmail.com>

Author: jonbartels