remove perf-tools (unmaintained since 2020) (#576)

README.md

@@ -658,7 +658,6 @@ Troubleshooting tools.
 - [grml](https://grml.org) - Bootable Debian Live CD with powerful CLI tools. ([Source Code](https://github.com/grml/)) `GPL-3.0` `Shell`
 - [mitmproxy](https://mitmproxy.org/) - A Python tool used for intercepting, viewing and modifying network traffic. Invaluable in troubleshooting certain problems. ([Source Code](https://github.com/mitmproxy/mitmproxy)) `MIT` `Python`
 - [mtr](https://www.bitwizard.nl/mtr/) - Network utility that combines traceroute and ping. ([Source Code](https://github.com/traviscross/mtr)) `GPL-2.0` `C`
-- [perf-tools](https://github.com/brendangregg/perf-tools) - Performance analysis tools based on Linux perf_events (aka perf) and ftrace. `GPL-2.0` `Shell`
 - [Sysdig](https://www.sysdig.com/) - Capture system state and activity from a running Linux instance, then save, filter and analyze. ([Source Code](https://github.com/draios/sysdig)) `Apache-2.0` `Docker/Lua/C`
 - [Wireshark](https://www.wireshark.org/) - The world's foremost network protocol analyzer. ([Source Code](https://gitlab.com/wireshark/wireshark)) `GPL-2.0` `C`