Get rid of bts singletons

There's no BTS single global object anymore, get rid of those APIs. Move
users to use "pcu->bts", which will evolve to a linked list in the
future.

Change-Id: I9cf762b0d3cb9e2cc3582727e07fa82c8e183ec5
diff --git a/tests/emu/pcu_emu.cpp b/tests/emu/pcu_emu.cpp
index ab2804b..d7b11ca 100644
--- a/tests/emu/pcu_emu.cpp
+++ b/tests/emu/pcu_emu.cpp
@@ -65,7 +65,7 @@
 
 static void init_main_bts()
 {
-	struct gprs_rlcmac_bts *bts = bts_main_data();
+	struct gprs_rlcmac_bts *bts = the_pcu->bts;
 	bts->initial_cs_dl = bts->initial_cs_ul = 1;
 	bts->cs_mask = 1 << 0; /* CS-1 always enabled by default */
 	bts->n3101 = 10;