* Remove use of deprecated PMD ruleset
This fixes annoying warnings we were getting during build.
- Use a custom PMD ruleset, since the built-in one uses deprecated rules.
- UnnecessaryImport replaces most of the deprecated rules
- Update maven-pmd-plugin to 3.15
- Exclude ancient asm version from caliper, since this was causing
incompatibility warnings with PMD and could also affect our tests runs
in unexpected ways
Xavier Léauté