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/src/Makefile.am b/src/Makefile.am
index 00b97d0..32cefc8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,13 +1,13 @@
 # This is _NOT_ the library release version, it's an API version.
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
-LIBVERSION=6:0:0
+LIBVERSION=7:0:0
 
 AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
-AM_CFLAGS = -Wall
+AM_CFLAGS = -Wall $(TALLOC_CFLAGS)
 
 lib_LTLIBRARIES = libosmocore.la
 
-libosmocore_la_LIBADD = $(BACKTRACE_LIB)
+libosmocore_la_LIBADD = $(BACKTRACE_LIB) $(TALLOC_LIBS)
 libosmocore_la_SOURCES = timer.c select.c signal.c msgb.c bits.c \
 			 bitvec.c statistics.c \
 			 write_queue.c utils.c socket.c \
@@ -21,15 +21,9 @@
 
 if ENABLE_PLUGIN
 libosmocore_la_SOURCES += plugin.c
-libosmocore_la_LDFLAGS = -version-info $(LIBVERSION) $(LIBRARY_DL) -no-undefined
+libosmocore_la_LDFLAGS = -version-info $(LIBVERSION) $(TALLOC_LIBS) $(LIBRARY_DL) -no-undefined
 else
-libosmocore_la_LDFLAGS = -version-info $(LIBVERSION) -no-undefined
-endif
-
-if ENABLE_TALLOC
-libosmocore_la_SOURCES += talloc.c
-else
-libosmocore_la_LIBADD += -ltalloc
+libosmocore_la_LDFLAGS = -version-info $(LIBVERSION) $(TALLOC_LIBS) -no-undefined
 endif
 
 if ENABLE_MSGFILE