Update requirements.txt

[matthewkotila]

Remove requirement of perf-analyzer since there are issues with macOS, and technically perf-analyzer is not needed for tritonclient

Let's relnote the fact that tritonclient users need to manually install perf-analyzer if they want it.

[whoisj]

@dmitry-tokarev-nv is this change no longer needed?

[dtpryce]

this would be handy for non-linux based users in downstream libraries that require tritonclient e.g. MLServer :D