perf(rustfs): remove the fake s3_operations benchmark (#4817)

bench(rustfs): remove the fake s3_operations benchmark

rustfs/benches/s3_operations.rs never measured S3: all three groups
(put_object/get_object/list_objects) only black_box(data.len())/black_box(count)
with a 'In a real benchmark, this would call the actual S3 client' comment. It
gave a false 'S3 operations have benchmark coverage' signal and was dead weight
on rustfs/Cargo.toml.

Delete the file and its [[bench]] entry. S3-face performance is covered solely
by the warp A/B gate (performance-ab.yml); the runbook scope note now says so
explicitly. Micro-benchmarks stay at the function level (perf-8).

Refs rustfs/backlog#1152 (perf-9).

rustfs/Cargo.toml

@@ -35,11 +35,6 @@ path = "src/lib.rs"
 name = "rustfs"
 path = "src/main.rs"
 
-[[bench]]
-name = "s3_operations"
-harness = false
-required-features = ["manual-test-runners"]
-
 [features]
 default = ["ftps", "webdav"]
 metrics-gpu = ["rustfs-obs/gpu"]