style: remove extra const keyword from interfaces

Const variables in prototypes don't add much value, but make the code
larger and redundant. Remove these const keywords.
Note, this doesn't apply to pointers to const memory.

src/sha1.c

@@ -206,9 +206,7 @@ void crypto_SHA1_Init(SHA1_CTX *context)
 }
 
 /* Run your data through this. */
-void crypto_SHA1_Update(SHA1_CTX *context,
-                        const uint8_t *data,
-                        const size_t len)
+void crypto_SHA1_Update(SHA1_CTX *context, const uint8_t *data, size_t len)
 {
     size_t i, j;