staging: rtl8188eu: Remove command _Set_H2C_MSG and its handler

_Set_H2C_MSG command is never issued by driver and its handler is a
dummy function.

Signed-off-by: navin patidar <navin.patidar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>