ci: use default Rust toolchain for JSON-RPC tests

Default preinstalled toolchain is currently at 1.65.0,
there is no need to overwrite it with 1.66.0 for these tests.

.github/workflows/jsonrpc.yml

@@ -19,11 +19,6 @@ jobs:
         uses: actions/setup-node@v3
         with:
           node-version: 16.x
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          override: true
       - name: Add Rust cache
         uses: Swatinem/rust-cache@v2
       - name: npm install