Fix Manager EventLog ClearLog Accept handling

The ClearLog action returns a JSON Redfish response, but it checks the
Accept header for application/octet-stream. This causes requests with
Accept: application/json to be marked as Bad Request.

The handler does not return after setting the error status, so it still
clears the log and returns a JSON success message. Remove the invalid
check to return the correct status.

Change-Id: Ica492e3185f970d39dd1655165ba623c5e7e29a4
Signed-off-by: Rex Fu <rex.fu@amd.com>