greybus: remove gb_i2c_retries_operation

Set retries operation was removed from the Greybus specification. Remove
gb_i2c_retries_operation and all other no longer necessary code bits from the
Greybus kernel code.

Signed-off-by: Michael Mogenson <michael.mogenson@leaflabs.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>