bts-trx: Don't reset transceiver_available in scheduler_trx.c
bts-trx: Don't reset transceiver_available in scheduler_trx.c

It can be dropped since bts_shutdown() ends up calling immediatelly
bts_model_trx_close() which in turn calls bts_model_trx_close() which
sets enabled = false and calls l1if_provision_transceiver_trx() to
power off the TRX.

Related: OS#4215
Change-Id: If8b3d2379d7ae102e1c338f4558ac1352de761cc

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