rust: remove out-of-date comment

We've migrated to a newer version of Rust, so it doesn't make sense anymore.

rust/hg-core/Cargo.toml

@@ -1,52 +1,50 b''
 [package]
 name = "hg-core"
 version = "0.1.0"
 authors = ["Georges Racinet <[e-mail]>"]
 description = "Mercurial pure Rust core library, with no assumption on Python bindings (FFI)"
 edition = "2021"
 
 [lib]
 name = "hg"
 
 [dependencies]
 bitflags = "1.3.2"
 bytes-cast = "0.3.0"
 byteorder = "1.4.3"
 derive_more = "0.99.17"
 hashbrown = { version = "0.13.1", features = ["rayon"] }
 home = "0.5.4"
 im-rc = "15.1.0"
 itertools = "0.10.5"
 lazy_static = "1.4.0"
 libc = "0.2.137"
 logging_timer = "1.1.0"
 ouroboros = "0.15.5"
 rand = "0.8.5"
 rand_pcg = "0.3.1"
 rand_distr = "0.4.3"
 rayon = "1.7.0"
 regex = "1.7.0"
 sha-1 = "0.10.0"
 twox-hash = "1.6.3"
 same-file = "1.0.6"
 tempfile = "3.3.0"
 thread_local = "1.1.4"
 crossbeam-channel = "0.5.6"
 log = "0.4.17"
 memmap2 = { version = "0.5.8", features = ["stable_deref_trait"] }
 zstd = "0.12"
 format-bytes = "0.3.0"
-# once_cell 1.15 uses edition 2021, while the heptapod CI
-# uses an old version of Cargo that doesn't support it.
 once_cell = "1.16.0"
 
 # We don't use the `miniz-oxide` backend to not change rhg benchmarks and until
 # we have a clearer view of which backend is the fastest.
 [dependencies.flate2]
 version = "1.0.24"
 features = ["zlib"]
 default-features = false
 
 [dev-dependencies]
 clap = { version = "4.0.24", features = ["derive"] }
 pretty_assertions = "1.1.0"