refactor: delete unreachable problem-flows wrapper

[chubes4]

Summary

• delete the unreachable GetProblemFlows model-tool wrapper
• preserve the canonical datamachine/get-problem-flows ability unchanged
• prove get_problem_flows remains absent from chat, pipeline-editor, and pipeline model resolution

Production LOC

• Added: 0 production PHP lines
• Deleted: 106 production PHP lines
• Net: -106 production PHP lines

No projection, replacement class, compatibility alias, registration change, REST change, CLI change, or capability change was added.

Verification

• authoritative WP Codebox focused suite: 6 passed, 0 failed (a1f2a389-0129-4889-aab1-36e992a0c17d)
• global ability projections: 41 assertions passed
• ability tool source: 48 assertions passed
• native ability execution: 47 assertions passed
• changed PHP syntax passes
• git diff --check passes

The candidate was produced by Homeboy Cook. Live controller promotion remains blocked because the merged wp-coding-agents DMC provider fix has not yet been installed on this host; the durable patch was reviewed and applied to the issue-owned managed worktree.

Closes #3374
Refs #3332
Parent: #3113