build: remove subdir-objects from configure.ac, it is broken

This is a known autoconf bug, it creates odd directories named literally
'$(top_srcdir)', potentially messing up dependency checking.

Change-Id: Ia47b038d4ca4f6c345711fb17d074f71c80e4453
diff --git a/configure.ac b/configure.ac
index 0c3ba3e..249701e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4,7 +4,7 @@
 
 LT_INIT
 
-AM_INIT_AUTOMAKE([foreign dist-bzip2 no-dist-gzip 1.9 subdir-objects tar-ustar])
+AM_INIT_AUTOMAKE([foreign dist-bzip2 no-dist-gzip 1.9 tar-ustar])
 dnl tar-ustar: some asn1 filenames surpass the 99 char limit of tar, so we need
 dnl to make tar allow longer filenames.