Remove node-tuning-and-monitoring.mdx — content owned by stacked PR #3178

This page is reviewed in the standalone stacked PR #3178 (branch
nitro-cli/node-tuning, base nitro-cli-guide) by @Jason-W123 and
@a-thomas-22. Removing it here so PR #3174 no longer duplicates the
content; PR #3178 re-adds it when it merges back into nitro-cli-guide.

Cross-references to /run-arbitrum-node/nitro/node-tuning-and-monitoring
from cli-flags-reference.mdx and scripts/generate-cli-reference.ts will
be temporarily broken on this branch until #3178 merges. Same pattern
as #3321 for configuration-system.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: anegg0