remove our internal copy of talloc, use system libtalloc

Shipping our own private copy of talloc was a good idea in 2008,
when it was not readily available on most target platforms.  Today,
the situation is quite different, as it is a standard library on
major Linux distributions.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 223535f..3dc9bd9 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1,5 +1,6 @@
 AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
-AM_CFLAGS = -Wall
+AM_CFLAGS = -Wall $(TALLOC_CFLAGS)
+AM_LDFLAGS = $(TALLOC_LIBS)
 
 check_PROGRAMS = timer/timer_test sms/sms_test ussd/ussd_test		\
                  smscb/smscb_test bits/bitrev_test a5/a5_test		\