OpenSK fuzzing path (#9889)

OpenSK moved its CTAP code into a library, and all fuzzing has moved
with it. As an advantage, we are now independent of other dependencies
that restricted the compiler versions we could use. Therefore, we are
now fuzzing on the latest nightly, hopefully fixing some issues that
came with the compiler restriction before.

The corresponding PR on our GitHub is
google/OpenSK#602

projects/opensk/build.sh

@@ -19,7 +19,7 @@ FUZZ_TARGET_OUTPUT_DIR=fuzz/target/x86_64-unknown-linux-gnu/release
 
 # do not use override toolchain
 # cf https://rust-lang.github.io/rustup/overrides.html
-export RUSTUP_TOOLCHAIN=nightly-2021-11-01
+export RUSTUP_TOOLCHAIN=nightly
 
 build_and_copy() {
   pushd "$1"
@@ -33,8 +33,8 @@ build_and_copy() {
 
 cd OpenSK
 
-# Main OpenSK fuzzing targets
-build_and_copy "."
+# CTAP library fuzzing targets
+build_and_copy libraries/opensk
 
 # persistent storage library
 build_and_copy libraries/persistent_store