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).

libraries/persistent_store/src/lib.rs

@@ -348,6 +348,7 @@
 #[macro_use]
 extern crate alloc;
 
+#[cfg(feature = "std")]
 mod buffer;
 #[cfg(feature = "std")]
 mod driver;
@@ -357,6 +358,7 @@ mod model;
 mod storage;
 mod store;
 
+#[cfg(feature = "std")]
 pub use self::buffer::{BufferCorruptFunction, BufferOptions, BufferStorage};
 #[cfg(feature = "std")]
 pub use self::driver::{