deps: remove 'num_cpus'

Now that std:🧵:available_parallelism is a thing, we no longer
need num_cpus.

Cargo.lock

@@ -340,16 +340,6 @@ dependencies = [
  "libc",
 ]
 
-[[package]]
-name = "num_cpus"
-version = "1.14.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f6058e64324c71e02bc2b150e4f3bc8286db6c83092132ffa3f6b1eab0f9def5"
-dependencies = [
- "hermit-abi",
- "libc",
-]
-
 [[package]]
 name = "once_cell"
 version = "1.16.0"
@@ -447,7 +437,6 @@ dependencies = [
  "jemallocator",
  "lazy_static",
  "log",
- "num_cpus",
  "regex",
  "serde",
  "serde_derive",