Fix once_cell dependency (#548)

* fixed version of once_cell

* fixes comments

* removes unnecessary fuzz dependency

Cargo.toml

@@ -45,6 +45,11 @@ sk-cbor = { path = "libraries/cbor" }
 uuid = { version = "0.8", features = ["v4"] }
 openssl = "0.10.36"
 
+# We explicitly lock the version of those transitive dependencies because their
+# Cargo.toml don't parse with the nightly compiler used by Tock. Remove this
+# whole block once CTAP is a library.
+once_cell = "=1.14" # transitive dependency of openssl
+
 [profile.dev]
 panic = "abort"
 lto = true # Link Time Optimization usually reduces size of binaries and static libraries