Don't add S-waiting-on-review label when perf finishes

[jyn514]

See #1502 for rationale. Fixes #1502

[jyn514]

CI failure looks unrelated.

[2022-11-30T17:36:53Z DEBUG collector::benchmark] Benchmark iteration 1/1
[2022-11-30T17:36:54Z INFO  collector::execute] run_rustc with incremental=false, profile=Debug, scenario=Some(Full), patch=None
file:///tmp/.tmpJ1kO4b#regex@1.5.5
[2022-11-30T17:36:54Z DEBUG collector::execute] "/home/runner/work/rustc-perf/rustc-perf/cache/90711a86e5bdd4b0b65d293f0c2c48fd2db761b3/bin/cargo" "llvm-lines" "--manifest-path" "Cargo.toml" "-p" "file:///tmp/.tmpJ1kO4b#regex@1.5.5" "--" "--wrap-rustc-with" "LlvmLines"
   Compiling memchr v2.4.0
   Compiling regex-syntax v0.6.25
"/home/runner/work/rustc-perf/rustc-perf/cache/90711a86e5bdd4b0b65d293f0c2c48fd2db761b3/bin/rustc" ["--crate-name", "build_script_build", "--edition=2018", "/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/memchr-2.4.0/build.rs", "--error-format=json", "--json=diagnostic-rendered-ansi,artifacts,future-incompat", "--crate-type", "bin", "--emit=dep-info,link", "-C", "embed-bitcode=no", "-C", "debuginfo=2", "--cfg", "feature=\"default\"", "--cfg", "feature=\"std\"", "-C", "metadata=61d92d470e3a1f78", "-C", "extra-filename=-61d92d470e3a1f78", "--out-dir", "/tmp/.tmpJ1kO4b/target/debug/build/memchr-61d92d470e3a1f78", "-L", "dependency=/tmp/.tmpJ1kO4b/target/debug/deps", "--cap-lints", "allow", "-Adeprecated", "-Aunknown-lints", "-Zincremental-verify-ich"]
exiting -- non-wrapped rustc
error: could not compile `memchr`

[nnethercote]

Makes sense.