ArmVirtPkg: Remove meaningless comment

ArmVirtPkg: Remove meaningless comment

The "Shell Embedded Boot Loader" description (added in
commit 6f5872b1f401) does not add any value, remove it.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Julien Grall <julien@xen.org>
Suggested-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>