remove pcu own bitvector implementation

The osmocore bitvec is exact the same, but use a pointer instead of
a reference.

Change-Id: Id8f797631d89aa12b6e48efb2dc153a3e2f059f7
diff --git a/src/gprs_bssgp_pcu.cpp b/src/gprs_bssgp_pcu.cpp
index c4ff402..7c325ae 100644
--- a/src/gprs_bssgp_pcu.cpp
+++ b/src/gprs_bssgp_pcu.cpp
@@ -90,7 +90,7 @@
 
 	LOGP(DBSSGP, LOGL_DEBUG, "Got BSSGP RA Capability of size %d\n", cap_len);
 
-	block = bitvec_alloc(cap_len);
+	block = bitvec_alloc(cap_len, tall_pcu_ctx);
 	bitvec_unpack(block, cap);
 
 	/* TS 24.008, 10.5.5.12a */