Remove ram_storage feature

We don't need to build a production key without persistent storage. Tests and
fuzzing continue to use the std feature to use the RAM implementation (that does
sanity checks).

.github/workflows/cargo_check.yml

@@ -66,12 +66,6 @@ jobs:
           command: check
           args: --target thumbv7em-none-eabi --release --features debug_allocations
 
-      - name: Check OpenSK ram_storage
-        uses: actions-rs/cargo@v1
-        with:
-          command: check
-          args: --target thumbv7em-none-eabi --release --features ram_storage
-
       - name: Check OpenSK verbose
         uses: actions-rs/cargo@v1
         with: