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).

src/embedded_flash/mod.rs

@@ -12,8 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#[cfg(not(any(test, feature = "ram_storage")))]
+#[cfg(not(feature = "std"))]
 mod syscall;
 
-#[cfg(not(any(test, feature = "ram_storage")))]
+#[cfg(not(feature = "std"))]
 pub use self::syscall::SyscallStorage;