performance: VerifyDuplicateTargets()

[Equanox]

This functions uses task.Target() which itself already loads BuildInfo. This adds a 100ms performance penalty. Reasons why this is a problem:

• task.Target()read buildinfo from proto file
• task.Target() triggers input.Hash generation
• input.Hash generation is calculated sequentially on this occasion (only the playbook executes in parallel)

Possible solution:
Use task.target instead of task.Target().