tokio: use single thread

Cargo.lock

@@ -991,16 +991,6 @@ dependencies = [
  "libm",
 ]
 
-[[package]]
-name = "num_cpus"
-version = "1.16.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4161fcb6d602d4d2081af7c3a45852d875a03dd337a6bfdd6e06407b61342a43"
-dependencies = [
- "hermit-abi",
- "libc",
-]
-
 [[package]]
 name = "object"
 version = "0.32.2"
@@ -1864,7 +1854,6 @@ dependencies = [
  "bytes",
  "libc",
  "mio",
- "num_cpus",
  "pin-project-lite",
  "socket2",
  "tokio-macros",