talloc: revert to use talloc inside libosmocore

It's not a good idea to confuse the two changes with each other.  Moving the
Abis part into a separate library is independent from the question whether we
have talloc inside libosmocore or use a stand-alone talloc library.
diff --git a/tests/ipa_proxy_test.c b/tests/ipa_proxy_test.c
index 755eec8..b57127a 100644
--- a/tests/ipa_proxy_test.c
+++ b/tests/ipa_proxy_test.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <talloc.h>
+#include <osmocom/core/talloc.h>
 #include <osmocom/abis/abis.h>
 #include <osmocom/abis/e1_input.h>
 #include <osmocom/abis/ipa_proxy.h>