Use a consistent version of fuzz_conversation() with all fuzzers.

Also undo a change to fuzz_sudoers.c that snuck in to the last commit.

lib/util/regress/fuzz/fuzz_sudo_conf.c

@@ -37,6 +37,25 @@ static int
 fuzz_conversation(int num_msgs, const struct sudo_conv_message msgs[],
     struct sudo_conv_reply replies[], struct sudo_conv_callback *callback)
 {
+    int n;
+
+    for (n = 0; n < num_msgs; n++) {
+	const struct sudo_conv_message *msg = &msgs[n];
+
+	switch (msg->msg_type & 0xff) {
+	    case SUDO_CONV_PROMPT_ECHO_ON:
+	    case SUDO_CONV_PROMPT_MASK:
+	    case SUDO_CONV_PROMPT_ECHO_OFF:
+		/* input not supported */
+		return -1;
+	    case SUDO_CONV_ERROR_MSG:
+	    case SUDO_CONV_INFO_MSG:
+		/* no output for fuzzers */
+		break;
+	    default:
+		return -1;
+	}
+    }
     return 0;
 }