Decommision src_common prior to reintroducing it for files common between eth and plugins

src/hash_bytes.h

@@ -0,0 +1,10 @@
+#ifndef HASH_BYTES_H_
+#define HASH_BYTES_H_
+
+#include <stdint.h>
+#include "cx.h"
+
+void hash_nbytes(const uint8_t *const bytes_ptr, size_t n, cx_hash_t *hash_ctx);
+void hash_byte(uint8_t byte, cx_hash_t *hash_ctx);
+
+#endif  // HASH_BYTES_H_