bsc: Move transaction.c from the libbsc to the libmsc

The BSC code does not use transactions, move it to the libmsc.
diff --git a/openbsc/src/libmsc/Makefile.am b/openbsc/src/libmsc/Makefile.am
index 17213ca..8d5034c 100644
--- a/openbsc/src/libmsc/Makefile.am
+++ b/openbsc/src/libmsc/Makefile.am
@@ -15,5 +15,6 @@
 			token_auth.c \
 			ussd.c \
 			vty_interface_layer3.c \
+			transaction.c \
 			osmo_msc.c