rgw: RGWRESTOp no longer tracks separate error code

rgw: RGWRESTOp no longer tracks separate error code

RGWOp_Bucket_Remove::execute() was storing failures from
bucket->remove_bucket() in op_ret, but left http_ret=0 so we responded
to the client with '200 OK'

to avoid bugs like this, remove the extra http_ret variable and only use
the op_ret from RGWOp

Signed-off-by: Casey Bodley <cbodley@redhat.com>