Revert "Libeinfo: do not suppress ewarn() messages"

This reverts commit 4ee62c7903.

The previously referenced commit broke consistency because ewarnx() was
respecting the EINFO_QUIET environment setting, but after this commit,
ewarn() was not.
Also, due to discussion on the below referenced bugs, I think we do
want to suppress warnings when EINFO_QUIET=yes.

X-Gentoo-Bug: 482396
X-Gentoo-Bug: 439174
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=482396
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=439174

src/libeinfo/libeinfo.c

@@ -705,7 +705,7 @@ ewarn(const char *EINFO_RESTRICT fmt, ...)
 	int retval;
 	va_list ap;
 
-	if (!fmt)
+	if (!fmt || is_quiet())
 		return 0;
 	va_start(ap, fmt);
 	elogv(LOG_WARNING, fmt, ap);