test: doc: remove `--perf` profiling from functional test framework #35528

This PR is an alternative to #35509. Rather than fixing, it removes the --perf option / profile_with_perf context manager features (both introduced in #14519) from the functional test framework. Given that no developer apparently even noticed that it's been broken for more than a year, we can conclude that it's largely unused and getting rid of it to reduce maintenance burden seems a reasonable choice. So far, neither in #35509 nor on IRC anyone has signaled strong interest to use or wanting to keep this feature.

The corresponding test documentation is removed as well, though the mentioning of perf profiling is still kept in the general developer docs -- only the reference to functional test framework integration is removed there.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35528.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #35509 (test: fix --perf profiling by theStack)
• #35395 (doc: Improve test suite dependencies documentation by hebasto)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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I saw this a while ago, but since it's not a cross-platform tool, I developed my own toolset since.

lightweight code review ACK 9fae7e98865c9f42c197b496b7d4896f0a92dff8

lgtm ACK 9fae7e98865c9f42c197b496b7d4896f0a92dff8 While this seems useful, no one using it is a good reason to remove it. If a user comes after this is merged, it should be trivial to revert.