MAINTAINERS: Delete invalid maintainer entries of the Exynos section

Mails to these e-mail addresses are rejected by the mail server
of Samsung with "User unknown" messages, so it seems like these
Exynos maintainers are no longer available.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 1459341140-16892-1-git-send-email-thuth@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
