MdeModulePkg: SmmLockBox: remove wrong DepEx

The SmmLockBox driver in
"MdeModulePkg/Universal/LockBox/SmmLockBox/SmmLockBox.inf" currently
specifies a DepEx on EFI_SMM_SW_DISPATCH2_PROTOCOL.

However, the driver doesn't use this protocol at all, either directly or
indirectly. It calls SmiHandlerRegister()
[MdeModulePkg/Core/PiSmmCore/Smi.c] to register SmmLockBoxHandler()
(which serves LockBox requests).

In turn, the SMM Core function SmiHandlerRegister() is also implemented
without EFI_SMM_SW_DISPATCH2_PROTOCOL.

The DepEx has been present since the initial commit of the SmmLockBox
driver (SVN r12029); it is probably superfluous. Let's remove it.

(Alternatively, we could extend OvmfPkg/EmuSmmDxe to fake this protocol,
and return EFI_UNSUPPORTED when any member is called.)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdeModulePkg@14930 6f19259b-4bc3-4df7-8a09-765794883524