Revert D50616780: [rust] upgrade toml_edit (0.19.8 -> 0.20.4) and tom…

…l (0.7.3 -> 0.8.4)

Test Plan: revert-hammer

Differential Revision:
D50616780

Original commit changeset: aa35720d2545

Original Phabricator Diff: D50616780

fbshipit-source-id: 632a66b97aaf25a04d6c329a6cfcdf337e1cdcf0

antlir/util/cli/json_arg/Cargo.toml

@@ -18,7 +18,7 @@ path = "src/lib.rs"
 [dependencies]
 serde = { version = "1.0.185", features = ["derive", "rc"] }
 serde_json = { version = "1.0.100", features = ["float_roundtrip", "unbounded_depth"] }
-toml = "0.8.4"
+toml = "0.7.3"
 
 [dev-dependencies]
 clap = { version = "3.2.25", features = ["derive", "env", "regex", "unicode", "wrap_help"] }