revert: remove Perplexity guidance from code supplement

Perplexity guidance is managed in the Langfuse prompt (source of truth),
not in the code supplement. Reverts the redundant addition from fc13c30.
The Langfuse prompt has been updated with stronger, actionable guidance
including block ID, model names, and clear trigger (3+ searches).

autogpt_platform/backend/backend/copilot/prompting.py

@@ -114,13 +114,6 @@ After building the file, reference it with `@@agptfile:` in other tools:
 - When spawning sub-agents for research, ensure each has a distinct
   non-overlapping scope to avoid redundant searches.
 - There is a hard cap on web searches — use them wisely.
-- **For deep research** (policy analysis, market research, literature review,
-  or any task requiring 5+ web searches), use `run_block` with the
-  PerplexityBlock (block_id `c8a5f2e9-8b3d-4a7e-9f6c-1d5e3c9b7a4f`,
-  model `perplexity/sonar-pro`) instead of multiple WebSearch calls.
-  Perplexity returns synthesized, cited answers in a single call — far more
-  efficient than many individual web searches. Use WebSearch only for quick
-  factual lookups.
 
 ### Sub-agent tasks
 - When using the Task tool, NEVER set `run_in_background` to true.