ci: remove protoc installation

With all crates have received a release since https://github.com/libp2p/rust-libp2p/issues/3024, building the baseline rustdoc no longer required `protoc` and we can thus remove it from our CI entirely.

Resolves #3539.

Pull-Request: #3858.

.github/workflows/ci.yml

@@ -31,8 +31,8 @@ jobs:
     env:
       CRATE: ${{ matrix.crate }}
     steps:
-      - name: Install Protoc
-        run: sudo apt-get install -y protobuf-compiler
+      - name: Install zlib for `libp2p-websocket` # https://github.com/paritytech/soketto/issues/72
+        run: sudo apt-get install zlib1g-dev --yes
 
       - uses: actions/checkout@v3
 

transports/websocket/src/lib.rs

@@ -52,6 +52,12 @@ use std::{
 ///
 /// If you don't need Secure Websocket's support, use a plain TCP transport as an inner transport.
 ///
+/// # Dependencies
+///
+/// This transport requires the `zlib` shared library to be installed on the system.
+///
+/// Future releases might lift this requirement, see <https://github.com/paritytech/soketto/issues/72>.
+///
 /// # Examples
 ///
 /// Secure Websocket transport: