debian: Depend directly on the two libraries needed for libosmo-abis

Do not pull in libosmocore but let the abis/trau library pull in
the DSO that is actually linked to.
diff --git a/debian/control b/debian/control
index 3621723..4d399a1 100644
--- a/debian/control
+++ b/debian/control
@@ -31,7 +31,7 @@
 Package: libosmo-abis-dev
 Section: libdevel
 Architecture: any
-Depends: ${misc:Depends}, libosmocore, libosmo-abis
+Depends: ${misc:Depends}, libosmotrau0, libosmoabis1
 Description: Development headers for A-bis interface.
 
 Package: libosmo-abis-dbg