internal, ssh: quiet unused RSA-only locals

Three locals feed only RSA and ECDSA code and draw -Werror warnings once
both are compiled out.

- digestSz in DoUserAuthRequestPublicKey(), read only by the RSA and
  ECDSA verify arms
- heap in SendKexGetSigningKey(), used only where a key is allocated
- the id parameter of CurveNameForId(), unread with no curve to name

src/internal.c

@@ -11648,6 +11648,9 @@ static int DoUserAuthRequestPublicKey(WOLFSSH* ssh, WS_UserAuthData* authData,
                     }
                 }
 
+                /* Only the RSA and ECDSA arms above read the digest size;
+                 * with both compiled out the switch is just the default. */
+                WOLFSSH_UNUSED(digestSz);
                 WS_FORCEZERO(digest, sizeof(digest));
             }
 
@@ -15736,6 +15739,8 @@ static int SendKexGetSigningKey(WOLFSSH* ssh,
 
 
     heap = ssh->ctx->heap;
+    /* Only the RSA, ECDSA and ML-DSA arms allocate; Ed25519 does not. */
+    WOLFSSH_UNUSED(heap);
 
 #ifdef WOLFSSH_TPM
     ssh->handshake->useTpm = ssh->ctx->privateKey[keyIdx].isTpm;

src/ssh.c

@@ -5488,6 +5488,8 @@ static const char* CurveNameForId(byte id)
             return "Curve25519";
 #endif
     }
+#else
+    WOLFSSH_UNUSED(id);
 #endif
     return "";
 }