build: Remove subdir-objects as it breaks make distclean

We are not using this option in any of our projects and it is breaking
make distclean. Remove the option for now.

make[2]: Entering directory `/openggsn-0.91/_build/ggsn'
Makefile:307: ../lib/.deps/getopt.Po: No such file or directory
Makefile:308: ../lib/.deps/getopt1.Po: No such file or directory
make[2]: *** No rule to make target `../lib/.deps/getopt1.Po'.  Stop.
diff --git a/ggsn/Makefile.am b/ggsn/Makefile.am
index 91aa726..ada5720 100644
--- a/ggsn/Makefile.am
+++ b/ggsn/Makefile.am
@@ -1,12 +1,10 @@
 bin_PROGRAMS = ggsn
 
-AUTOMAKE_OPTIONS = subdir-objects
-
 AM_LDFLAGS = @EXEC_LDFLAGS@
 
 AM_CFLAGS = -O2 -D_GNU_SOURCE -fno-builtin -Wall -DSBINDIR='"$(sbindir)"' -ggdb
 
-ggsn_LDADD = @LIBOBJS@ @EXEC_LDADD@ -lgtp -L../gtp ../lib/libmisc.a
+ggsn_LDADD = @EXEC_LDADD@ -lgtp -L../gtp ../lib/libmisc.a
 ggsn_DEPENDENCIES = ../gtp/libgtp.la ../lib/libmisc.a
 ggsn_SOURCES = ggsn.c cmdline.c cmdline.h