Use std::cell::OnceCell and remove mitochondria dependency (#30207)

`OnceCell` is now part of the standard library and we'll be able to use
it once we upgrade rust. For now we can use the version that's shipped
behind a feature flag in rust. This removes a dependency on one crate.

Cargo.lock

@@ -3129,7 +3129,6 @@ dependencies = [
  "lazy_static",
  "libc",
  "log",
- "mitochondria",
  "msg",
  "net_traits",
  "parking_lot",
@@ -3735,12 +3734,6 @@ dependencies = [
  "winapi",
 ]
 
-[[package]]
-name = "mitochondria"
-version = "1.1.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9de3eca27871df31c33b807f834b94ef7d000956f57aa25c5aed9c5f0aae8f6f"
-
 [[package]]
 name = "mozangle"
 version = "0.3.5"
@@ -4991,7 +4984,6 @@ dependencies = [
  "metrics",
  "mime",
  "mime_guess",
- "mitochondria",
  "mozangle",
  "mozjs",
  "msg",