esmtp: remove sendmail from sysroot

The sysroot/${libdir}/sendmail conflicts with lsb's, and it's a
symlink to ${bindir}/esmtp which is meaningless for sysroot, so
remove it.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>