Extract duplicated code detector to rector/swiss-knife

[TomasVotruba]

The token-based copy-paste detector in utils/duplicates is now a reusable duplicated-code command in rector/swiss-knife.

This removes the local utils/duplicates script and points the duplicated-code composer script at the swiss-knife command instead:

vendor/bin/swiss-knife duplicated-code src rules --min-tokens 150 --min-lines 5

The Duplicated Code CI job is unchanged - it still runs composer duplicated-code.

Note: needs swiss-knife rectorphp/swiss-knife#137 released first.