fix test code being unnecessarily feature gated

These cfg attributes were here because these tests used the `vec!` macro
in the past.

hashes/src/hash160.rs

@@ -55,7 +55,6 @@ mod tests {
         use crate::{hash160, HashEngine};
 
         #[derive(Clone)]
-        #[cfg(feature = "alloc")]
         struct Test {
             input: [u8; 65],
             output: [u8; 20],

hashes/src/hmac.rs

@@ -164,7 +164,6 @@ impl<'de, T: GeneralHash + Deserialize<'de>> Deserialize<'de> for Hmac<T> {
 #[cfg(test)]
 mod tests {
     #[test]
-    #[cfg(feature = "alloc")]
     fn test() {
         use crate::{sha256, GeneralHash as _, Hash as _, HashEngine, Hmac, HmacEngine};