struct gsm_bts_trx: remove unused per-TRX OML Link pointer
struct gsm_bts_trx: remove unused per-TRX OML Link pointer

Most likely, this part of the structure was copy-pasted from the
corresponding definition in osmo-bsc.  In osmo-bts we always
establish a single per-BTS OML link, not per-TRX.

Change-Id: I1792372de484608e04211c9de4294b3c76173ead

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts