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

man/einfo.3

@@ -105,7 +105,8 @@ and
 respectively, but only work when
 .Va EINFO_VERBOSE
 is true. You can also make the
-.Fn einfo
+.Fn einfo ,
+.Fn ewarn ,
 and
 .Fn ebegin
 functions silent by setting