upstream: improve the error message for u2f enrollment errors by

making ssh-keygen be solely responsible for printing the error message and
convertint some more common error responses from the middleware to a useful
ssherr.h status code. more detail remains visible via -v of course.

also remove indepedent copy of sk-api.h declarations in sk-usbhid.c
and just include it.

feedback & ok markus@

OpenBSD-Commit-ID: a4a8ffa870d9a3e0cfd76544bcdeef5c9fb1f1bb
diff --git a/ssherr.h b/ssherr.h
index 520bd49..085e752 100644
--- a/ssherr.h
+++ b/ssherr.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ssherr.h,v 1.7 2019/12/30 09:24:45 djm Exp $	*/
+/*	$OpenBSD: ssherr.h,v 1.8 2020/01/25 23:13:09 djm Exp $	*/
 /*
  * Copyright (c) 2011 Damien Miller
  *
@@ -81,6 +81,7 @@
 #define SSH_ERR_NUMBER_TOO_LARGE		-57
 #define SSH_ERR_SIGN_ALG_UNSUPPORTED		-58
 #define SSH_ERR_FEATURE_UNSUPPORTED		-59
+#define SSH_ERR_DEVICE_NOT_FOUND		-60
 
 /* Translate a numeric error code to a human-readable error string */
 const char *ssh_err(int n);