bsc/osmo-bsc.cfg: remove legacy 'rtp-base' config

osmo-bsc does not use an rtp-base for years, ever since we're using an MGW.

Related: Id14fa3066ca5d472a817593074a6222f159168a8
Change-Id: Ia4866fc603877b2ab8ce16683e9f6145764117c7
diff --git a/bsc/osmo-bsc.cfg b/bsc/osmo-bsc.cfg
index f490433..cd698b0 100644
--- a/bsc/osmo-bsc.cfg
+++ b/bsc/osmo-bsc.cfg
@@ -367,7 +367,6 @@
    timeslot 7
     phys_chan_config PDCH
 msc 0
- ip.access rtp-base 4000
  no bsc-welcome-text
  no bsc-msc-lost-text
  no bsc-grace-text