greybus: svc: remove input device handling in SVC protocol

The input device was added before to handle the key(s) connected
directly to SVC, which is not the case anymore. So, this change removes
the gb_svc_key_event() operation and the corresponding input device
code with it.

Testing Done:
Boot tested and tried module insert/removal through AraManager

Change-Id: Iaa541d4aefb5c0ed16caaa39450029de35d7c228
Signed-off-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>